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# commit db9b4570c5dc550074140ac1d1677077fba29a26
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# Author: Alan Modra <amodra@gmail.com>
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# Date: Sat Aug 17 18:40:11 2013 +0930
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#
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# PowerPC LE strlen
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# http://sourceware.org/ml/libc-alpha/2013-08/msg00097.html
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#
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# This is the first of nine patches adding little-endian support to the
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# existing optimised string and memory functions. I did spend some
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# time with a power7 simulator looking at cycle by cycle behaviour for
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# memchr, but most of these patches have not been run on cpu simulators
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# to check that we are going as fast as possible. I'm sure PowerPC can
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# do better. However, the little-endian support mostly leaves main
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# loops unchanged, so I'm banking on previous authors having done a
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# good job on big-endian.. As with most code you stare at long enough,
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# I found some improvements for big-endian too.
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#
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# Little-endian support for strlen. Like most of the string functions,
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# I leave the main word or multiple-word loops substantially unchanged,
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# just needing to modify the tail.
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#
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# Removing the branch in the power7 functions is just a tidy. .align
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# produces a branch anyway. Modifying regs in the non-power7 functions
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# is to suit the new little-endian tail.
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#
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# * sysdeps/powerpc/powerpc64/power7/strlen.S (strlen): Add little-endian
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# support. Don't branch over align.
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# * sysdeps/powerpc/powerpc32/power7/strlen.S: Likewise.
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# * sysdeps/powerpc/powerpc64/strlen.S (strlen): Add little-endian support.
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# Rearrange tmp reg use to suit. Comment.
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# * sysdeps/powerpc/powerpc32/strlen.S: Likewise.
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#
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diff -urN glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/power7/strlen.S glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/power7/strlen.S
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--- glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/power7/strlen.S 2014-05-28 12:28:44.000000000 -0500
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+++ glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/power7/strlen.S 2014-05-28 12:28:45.000000000 -0500
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@@ -31,7 +31,11 @@
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li r0,0 /* Word with null chars to use with cmpb. */
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li r5,-1 /* MASK = 0xffffffffffffffff. */
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lwz r12,0(r4) /* Load word from memory. */
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+#ifdef __LITTLE_ENDIAN__
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+ slw r5,r5,r6
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+#else
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srw r5,r5,r6 /* MASK = MASK >> padding. */
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+#endif
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orc r9,r12,r5 /* Mask bits that are not part of the string. */
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cmpb r10,r9,r0 /* Check for null bytes in WORD1. */
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cmpwi cr7,r10,0 /* If r10 == 0, no null's have been found. */
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@@ -49,9 +53,6 @@
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cmpb r10,r12,r0
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cmpwi cr7,r10,0
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bne cr7,L(done)
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- b L(loop) /* We branch here (rather than falling through)
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- to skip the nops due to heavy alignment
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- of the loop below. */
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/* Main loop to look for the end of the string. Since it's a
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small loop (< 8 instructions), align it to 32-bytes. */
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@@ -88,9 +89,15 @@
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0xff in the same position as the null byte in the original
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word from the string. Use that to calculate the length. */
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L(done):
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- cntlzw r0,r10 /* Count leading zeroes before the match. */
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+#ifdef __LITTLE_ENDIAN__
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+ addi r9, r10, -1 /* Form a mask from trailing zeros. */
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+ andc r9, r9, r10
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+ popcntw r0, r9 /* Count the bits in the mask. */
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+#else
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+ cntlzw r0,r10 /* Count leading zeros before the match. */
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+#endif
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subf r5,r3,r4
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- srwi r0,r0,3 /* Convert leading zeroes to bytes. */
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+ srwi r0,r0,3 /* Convert leading zeros to bytes. */
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add r3,r5,r0 /* Compute final length. */
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blr
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END (BP_SYM (strlen))
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diff -urN glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/strlen.S glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/strlen.S
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--- glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/strlen.S 2014-05-28 12:28:44.000000000 -0500
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+++ glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/strlen.S 2014-05-28 12:32:24.000000000 -0500
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@@ -31,7 +31,12 @@
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1 is subtracted you get a value in the range 0x00-0x7f, none of which
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have their high bit set. The expression here is
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(x + 0xfefefeff) & ~(x | 0x7f7f7f7f), which gives 0x00000000 when
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- there were no 0x00 bytes in the word.
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+ there were no 0x00 bytes in the word. You get 0x80 in bytes that
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+ match, but possibly false 0x80 matches in the next more significant
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+ byte to a true match due to carries. For little-endian this is
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+ of no consequence since the least significant match is the one
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+ we're interested in, but big-endian needs method 2 to find which
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+ byte matches.
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2) Given a word 'x', we can test to see _which_ byte was zero by
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calculating ~(((x & 0x7f7f7f7f) + 0x7f7f7f7f) | x | 0x7f7f7f7f).
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@@ -74,7 +79,7 @@
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ENTRY (BP_SYM (strlen))
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-#define rTMP1 r0
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+#define rTMP4 r0
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#define rRTN r3 /* incoming STR arg, outgoing result */
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#define rSTR r4 /* current string position */
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#define rPADN r5 /* number of padding bits we prepend to the
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@@ -84,9 +89,9 @@
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#define rWORD1 r8 /* current string word */
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#define rWORD2 r9 /* next string word */
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#define rMASK r9 /* mask for first string word */
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-#define rTMP2 r10
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-#define rTMP3 r11
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-#define rTMP4 r12
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+#define rTMP1 r10
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+#define rTMP2 r11
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+#define rTMP3 r12
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CHECK_BOUNDS_LOW (rRTN, rTMP1, rTMP2)
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@@ -96,15 +101,20 @@
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lwz rWORD1, 0(rSTR)
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li rMASK, -1
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addi r7F7F, r7F7F, 0x7f7f
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-/* That's the setup done, now do the first pair of words.
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- We make an exception and use method (2) on the first two words, to reduce
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- overhead. */
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+/* We use method (2) on the first two words, because rFEFE isn't
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+ required which reduces setup overhead. Also gives a faster return
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+ for small strings on big-endian due to needing to recalculate with
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+ method (2) anyway. */
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+#ifdef __LITTLE_ENDIAN__
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+ slw rMASK, rMASK, rPADN
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+#else
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srw rMASK, rMASK, rPADN
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+#endif
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and rTMP1, r7F7F, rWORD1
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or rTMP2, r7F7F, rWORD1
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add rTMP1, rTMP1, r7F7F
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- nor rTMP1, rTMP2, rTMP1
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- and. rWORD1, rTMP1, rMASK
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+ nor rTMP3, rTMP2, rTMP1
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+ and. rTMP3, rTMP3, rMASK
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mtcrf 0x01, rRTN
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bne L(done0)
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lis rFEFE, -0x101
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@@ -113,11 +123,12 @@
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bt 29, L(loop)
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/* Handle second word of pair. */
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+/* Perhaps use method (1) here for little-endian, saving one instruction? */
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lwzu rWORD1, 4(rSTR)
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and rTMP1, r7F7F, rWORD1
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or rTMP2, r7F7F, rWORD1
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add rTMP1, rTMP1, r7F7F
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- nor. rWORD1, rTMP2, rTMP1
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+ nor. rTMP3, rTMP2, rTMP1
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bne L(done0)
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/* The loop. */
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@@ -131,29 +142,53 @@
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add rTMP3, rFEFE, rWORD2
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nor rTMP4, r7F7F, rWORD2
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bne L(done1)
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- and. rTMP1, rTMP3, rTMP4
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+ and. rTMP3, rTMP3, rTMP4
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beq L(loop)
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+#ifndef __LITTLE_ENDIAN__
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and rTMP1, r7F7F, rWORD2
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add rTMP1, rTMP1, r7F7F
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- andc rWORD1, rTMP4, rTMP1
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+ andc rTMP3, rTMP4, rTMP1
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b L(done0)
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L(done1):
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and rTMP1, r7F7F, rWORD1
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subi rSTR, rSTR, 4
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add rTMP1, rTMP1, r7F7F
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- andc rWORD1, rTMP2, rTMP1
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+ andc rTMP3, rTMP2, rTMP1
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/* When we get to here, rSTR points to the first word in the string that
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- contains a zero byte, and the most significant set bit in rWORD1 is in that
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- byte. */
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+ contains a zero byte, and rTMP3 has 0x80 for bytes that are zero,
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+ and 0x00 otherwise. */
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L(done0):
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- cntlzw rTMP3, rWORD1
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+ cntlzw rTMP3, rTMP3
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subf rTMP1, rRTN, rSTR
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srwi rTMP3, rTMP3, 3
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add rRTN, rTMP1, rTMP3
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/* GKM FIXME: check high bound. */
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blr
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+#else
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+
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+L(done0):
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+ addi rTMP1, rTMP3, -1 /* Form a mask from trailing zeros. */
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+ andc rTMP1, rTMP1, rTMP3
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+ cntlzw rTMP1, rTMP1 /* Count bits not in the mask. */
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+ subf rTMP3, rRTN, rSTR
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+ subfic rTMP1, rTMP1, 32-7
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+ srwi rTMP1, rTMP1, 3
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+ add rRTN, rTMP1, rTMP3
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+ blr
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+
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+L(done1):
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+ addi rTMP3, rTMP1, -1
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+ andc rTMP3, rTMP3, rTMP1
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+ cntlzw rTMP3, rTMP3
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+ subf rTMP1, rRTN, rSTR
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+ subfic rTMP3, rTMP3, 32-7-32
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+ srawi rTMP3, rTMP3, 3
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+ add rRTN, rTMP1, rTMP3
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+ blr
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+#endif
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+
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END (BP_SYM (strlen))
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libc_hidden_builtin_def (strlen)
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diff -urN glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/power7/strlen.S glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/power7/strlen.S
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--- glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/power7/strlen.S 2014-05-28 12:28:44.000000000 -0500
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+++ glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/power7/strlen.S 2014-05-28 12:28:45.000000000 -0500
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@@ -32,7 +32,11 @@
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with cmpb. */
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li r5,-1 /* MASK = 0xffffffffffffffff. */
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ld r12,0(r4) /* Load doubleword from memory. */
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+#ifdef __LITTLE_ENDIAN__
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+ sld r5,r5,r6
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+#else
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srd r5,r5,r6 /* MASK = MASK >> padding. */
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+#endif
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orc r9,r12,r5 /* Mask bits that are not part of the string. */
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cmpb r10,r9,r0 /* Check for null bytes in DWORD1. */
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cmpdi cr7,r10,0 /* If r10 == 0, no null's have been found. */
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@@ -50,9 +54,6 @@
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cmpb r10,r12,r0
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cmpdi cr7,r10,0
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bne cr7,L(done)
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- b L(loop) /* We branch here (rather than falling through)
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- to skip the nops due to heavy alignment
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- of the loop below. */
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/* Main loop to look for the end of the string. Since it's a
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small loop (< 8 instructions), align it to 32-bytes. */
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@@ -89,9 +90,15 @@
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0xff in the same position as the null byte in the original
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doubleword from the string. Use that to calculate the length. */
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L(done):
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- cntlzd r0,r10 /* Count leading zeroes before the match. */
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+#ifdef __LITTLE_ENDIAN__
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+ addi r9, r10, -1 /* Form a mask from trailing zeros. */
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+ andc r9, r9, r10
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+ popcntd r0, r9 /* Count the bits in the mask. */
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+#else
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+ cntlzd r0,r10 /* Count leading zeros before the match. */
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+#endif
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subf r5,r3,r4
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- srdi r0,r0,3 /* Convert leading zeroes to bytes. */
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+ srdi r0,r0,3 /* Convert leading/trailing zeros to bytes. */
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add r3,r5,r0 /* Compute final length. */
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blr
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END (BP_SYM (strlen))
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12745e |
diff -urN glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/strlen.S glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/strlen.S
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12745e |
--- glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/strlen.S 2014-05-28 12:28:44.000000000 -0500
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+++ glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/strlen.S 2014-05-28 12:38:17.000000000 -0500
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@@ -31,7 +31,12 @@
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1 is subtracted you get a value in the range 0x00-0x7f, none of which
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have their high bit set. The expression here is
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(x + 0xfefefeff) & ~(x | 0x7f7f7f7f), which gives 0x00000000 when
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- there were no 0x00 bytes in the word.
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+ there were no 0x00 bytes in the word. You get 0x80 in bytes that
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+ match, but possibly false 0x80 matches in the next more significant
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+ byte to a true match due to carries. For little-endian this is
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+ of no consequence since the least significant match is the one
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+ we're interested in, but big-endian needs method 2 to find which
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+ byte matches.
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2) Given a word 'x', we can test to see _which_ byte was zero by
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calculating ~(((x & 0x7f7f7f7f) + 0x7f7f7f7f) | x | 0x7f7f7f7f).
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@@ -64,7 +69,7 @@
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Answer:
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1) Added a Data Cache Block Touch early to prefetch the first 128
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byte cache line. Adding dcbt instructions to the loop would not be
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- effective since most strings will be shorter than the cache line.*/
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+ effective since most strings will be shorter than the cache line. */
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/* Some notes on register usage: Under the SVR4 ABI, we can use registers
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0 and 3 through 12 (so long as we don't call any procedures) without
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@@ -80,7 +85,7 @@
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ENTRY (BP_SYM (strlen))
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CALL_MCOUNT 1
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-#define rTMP1 r0
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+#define rTMP4 r0
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#define rRTN r3 /* incoming STR arg, outgoing result */
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#define rSTR r4 /* current string position */
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#define rPADN r5 /* number of padding bits we prepend to the
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@@ -90,9 +95,9 @@
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#define rWORD1 r8 /* current string doubleword */
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#define rWORD2 r9 /* next string doubleword */
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#define rMASK r9 /* mask for first string doubleword */
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-#define rTMP2 r10
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-#define rTMP3 r11
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-#define rTMP4 r12
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+#define rTMP1 r10
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+#define rTMP2 r11
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+#define rTMP3 r12
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/* Note: The Bounded pointer support in this code is broken. This code
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was inherited from PPC32 and that support was never completed.
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@@ -109,30 +114,36 @@
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addi r7F7F, r7F7F, 0x7f7f
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li rMASK, -1
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insrdi r7F7F, r7F7F, 32, 0
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-/* That's the setup done, now do the first pair of doublewords.
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- We make an exception and use method (2) on the first two doublewords,
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- to reduce overhead. */
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- srd rMASK, rMASK, rPADN
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+/* We use method (2) on the first two doublewords, because rFEFE isn't
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+ required which reduces setup overhead. Also gives a faster return
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+ for small strings on big-endian due to needing to recalculate with
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+ method (2) anyway. */
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+#ifdef __LITTLE_ENDIAN__
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+ sld rMASK, rMASK, rPADN
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+#else
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+ srd rMASK, rMASK, rPADN
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+#endif
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and rTMP1, r7F7F, rWORD1
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or rTMP2, r7F7F, rWORD1
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lis rFEFE, -0x101
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add rTMP1, rTMP1, r7F7F
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addi rFEFE, rFEFE, -0x101
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- nor rTMP1, rTMP2, rTMP1
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- and. rWORD1, rTMP1, rMASK
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+ nor rTMP3, rTMP2, rTMP1
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+ and. rTMP3, rTMP3, rMASK
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mtcrf 0x01, rRTN
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bne L(done0)
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- sldi rTMP1, rFEFE, 32
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- add rFEFE, rFEFE, rTMP1
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+ sldi rTMP1, rFEFE, 32
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+ add rFEFE, rFEFE, rTMP1
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/* Are we now aligned to a doubleword boundary? */
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bt 28, L(loop)
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/* Handle second doubleword of pair. */
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+/* Perhaps use method (1) here for little-endian, saving one instruction? */
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ldu rWORD1, 8(rSTR)
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and rTMP1, r7F7F, rWORD1
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or rTMP2, r7F7F, rWORD1
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add rTMP1, rTMP1, r7F7F
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- nor. rWORD1, rTMP2, rTMP1
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+ nor. rTMP3, rTMP2, rTMP1
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bne L(done0)
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/* The loop. */
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@@ -146,29 +157,53 @@
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add rTMP3, rFEFE, rWORD2
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nor rTMP4, r7F7F, rWORD2
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bne L(done1)
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- and. rTMP1, rTMP3, rTMP4
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+ and. rTMP3, rTMP3, rTMP4
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beq L(loop)
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+#ifndef __LITTLE_ENDIAN__
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and rTMP1, r7F7F, rWORD2
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add rTMP1, rTMP1, r7F7F
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- andc rWORD1, rTMP4, rTMP1
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+ andc rTMP3, rTMP4, rTMP1
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b L(done0)
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L(done1):
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and rTMP1, r7F7F, rWORD1
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subi rSTR, rSTR, 8
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add rTMP1, rTMP1, r7F7F
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- andc rWORD1, rTMP2, rTMP1
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+ andc rTMP3, rTMP2, rTMP1
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/* When we get to here, rSTR points to the first doubleword in the string that
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- contains a zero byte, and the most significant set bit in rWORD1 is in that
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- byte. */
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+ contains a zero byte, and rTMP3 has 0x80 for bytes that are zero, and 0x00
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+ otherwise. */
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L(done0):
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- cntlzd rTMP3, rWORD1
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+ cntlzd rTMP3, rTMP3
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subf rTMP1, rRTN, rSTR
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srdi rTMP3, rTMP3, 3
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add rRTN, rTMP1, rTMP3
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/* GKM FIXME: check high bound. */
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blr
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+#else
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+
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+L(done0):
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+ addi rTMP1, rTMP3, -1 /* Form a mask from trailing zeros. */
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+ andc rTMP1, rTMP1, rTMP3
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+ cntlzd rTMP1, rTMP1 /* Count bits not in the mask. */
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+ subf rTMP3, rRTN, rSTR
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+ subfic rTMP1, rTMP1, 64-7
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+ srdi rTMP1, rTMP1, 3
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+ add rRTN, rTMP1, rTMP3
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+ blr
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+
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+L(done1):
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+ addi rTMP3, rTMP1, -1
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+ andc rTMP3, rTMP3, rTMP1
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+ cntlzd rTMP3, rTMP3
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+ subf rTMP1, rRTN, rSTR
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+ subfic rTMP3, rTMP3, 64-7-64
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+ sradi rTMP3, rTMP3, 3
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+ add rRTN, rTMP1, rTMP3
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+ blr
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+#endif
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+
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END (BP_SYM (strlen))
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libc_hidden_builtin_def (strlen)
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