Backport of this upstream commit (with libm-test.inc adjustments): commit c7de50250367167d8c9f35594b264f6a0af8dd0c Author: Adhemerval Zanella Date: Fri Mar 14 12:49:45 2014 -0500 PowerPC: remove wrong roundl implementation for PowerPC64 The roundl assembly implementation (sysdeps/powerpc/powerpc64/fpu/s_roundl.S) returns wrong results for some inputs where first double is a exact integer and the precision is determined by second long double. Checking on implementation comments and history, I am very confident the assembly implementation was based on a version before commit 5c68d401698a58cf7da150d9cce769fa6679ba5f that fixes BZ#2423 (Errors in long double (ldbl-128ibm) rounding functions in glibc-2.4). By just removing the implementation and make the build select sysdeps/ieee754/ldbl-128ibm/s_roundl.c instead fixes the failing math. This fixes 16707. Index: b/math/libm-test.inc =================================================================== --- a/math/libm-test.inc +++ b/math/libm-test.inc @@ -9268,6 +9268,15 @@ round_test (void) TEST_f_f (round, -72057594037927936.75L, -72057594037927937.0L); TEST_f_f (round, -72057594037927937.5L, -72057594037927938.0L); + /* Check cases where first double is a exact integer higher than 2^52 and + the precision is determined by second long double for IBM long double. */ + TEST_f_f (round, 34503599627370498.515625L, 34503599627370499.0L); + TEST_f_f (round, -34503599627370498.515625L, -34503599627370499.0L); +# if LDBL_MANT_DIG >= 106 + TEST_f_f (round, 1192568192774434123539907640624.484375L, 1192568192774434123539907640624.0L); + TEST_f_f (round, -1192568192774434123539907640624.484375L, -1192568192774434123539907640624.0L); +# endif + TEST_f_f (round, 10141204801825835211973625643007.5L, 10141204801825835211973625643008.0L); TEST_f_f (round, 10141204801825835211973625643008.25L, 10141204801825835211973625643008.0L); TEST_f_f (round, 10141204801825835211973625643008.5L, 10141204801825835211973625643009.0L); Index: b/sysdeps/powerpc/powerpc64/fpu/s_roundl.S =================================================================== --- a/sysdeps/powerpc/powerpc64/fpu/s_roundl.S +++ /dev/null @@ -1,132 +0,0 @@ -/* long double round function. - IBM extended format long double version. - Copyright (C) 2004, 2006 Free Software Foundation, Inc. - This file is part of the GNU C Library. - - The GNU C Library is free software; you can redistribute it and/or - modify it under the terms of the GNU Lesser General Public - License as published by the Free Software Foundation; either - version 2.1 of the License, or (at your option) any later version. - - The GNU C Library is distributed in the hope that it will be useful, - but WITHOUT ANY WARRANTY; without even the implied warranty of - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU - Lesser General Public License for more details. - - You should have received a copy of the GNU Lesser General Public - License along with the GNU C Library; if not, see - . */ - -#include -#include - - .section ".toc","aw" -.LC0: /* 2**52 */ - .tc FD_43300000_0[TC],0x4330000000000000 -.LC1: /* 0.5 */ - .tc FD_3fe00000_0[TC],0x3fe0000000000000 - .section ".text" - -/* long double [fp1,fp2] roundl (long double x [fp1,fp2]) - IEEE 1003.1 round function. IEEE specifies "round to the nearest - integer value, rounding halfway cases away from zero, regardless of - the current rounding mode." However PowerPC Architecture defines - "Round to Nearest" as "Choose the best approximation. In case of a - tie, choose the one that is even (least significant bit o).". - So we can't use the PowerPC "Round to Nearest" mode. Instead we set - "Round toward Zero" mode and round by adding +-0.5 before rounding - to the integer value. */ - -ENTRY (__roundl) - mffs fp11 /* Save current FPU rounding mode. */ - lfd fp13,.LC0@toc(2) - fabs fp0,fp1 - fabs fp9,fp2 - fsub fp12,fp13,fp13 /* generate 0.0 */ - fcmpu cr7,fp0,fp13 /* if (fabs(x) > TWO52) */ - fcmpu cr6,fp1,fp12 /* if (x > 0.0) */ - bnl- cr7,.L2 - mtfsfi 7,1 /* Set rounding mode toward 0. */ - lfd fp10,.LC1@toc(2) - ble- cr6,.L1 - fneg fp2,fp12 - fadd fp1,fp1,fp10 /* x+= 0.5; */ - fadd fp1,fp1,fp13 /* x+= TWO52; */ - fsub fp1,fp1,fp13 /* x-= TWO52; */ - fabs fp1,fp1 /* if (x == 0.0) x = 0.0; */ -.L0: - mtfsf 0x01,fp11 /* restore previous rounding mode. */ - blr -.L1: - fsub fp9,fp1,fp10 /* x-= 0.5; */ - fneg fp2,fp12 - bge- cr6,.L0 /* if (x < 0.0) */ - fsub fp1,fp9,fp13 /* x-= TWO52; */ - fadd fp1,fp1,fp13 /* x+= TWO52; */ - fnabs fp1,fp1 /* if (x == 0.0) x = -0.0; */ - mtfsf 0x01,fp11 /* restore previous rounding mode. */ - blr - -/* The high double is > TWO52 so we need to round the low double and - perhaps the high double. In this case we have to round the low - double and handle any adjustment to the high double that may be - caused by rounding (up). This is complicated by the fact that the - high double may already be rounded and the low double may have the - opposite sign to compensate.This gets a bit tricky so we use the - following algorithm: - - tau = floor(x_high/TWO52); - x0 = x_high - tau; - x1 = x_low + tau; - r1 = rint(x1); - y_high = x0 + r1; - y_low = x0 - y_high + r1; - return y; */ -.L2: - fcmpu cr7,fp9,fp13 /* if (|x_low| > TWO52) */ - fcmpu cr0,fp9,fp12 /* || (|x_low| == 0.0) */ - fcmpu cr5,fp2,fp12 /* if (x_low > 0.0) */ - lfd fp10,.LC1@toc(2) - bgelr- cr7 /* return x; */ - beqlr- cr0 - mtfsfi 7,1 /* Set rounding mode toward 0. */ - fdiv fp8,fp1,fp13 /* x_high/TWO52 */ - - bng- cr6,.L6 /* if (x > 0.0) */ - fctidz fp0,fp8 - fcfid fp8,fp0 /* tau = floor(x_high/TWO52); */ - bng cr5,.L4 /* if (x_low > 0.0) */ - fmr fp3,fp1 - fmr fp4,fp2 - b .L5 -.L4: /* if (x_low < 0.0) */ - fsub fp3,fp1,fp8 /* x0 = x_high - tau; */ - fadd fp4,fp2,fp8 /* x1 = x_low + tau; */ -.L5: - fadd fp5,fp4,fp10 /* r1 = x1 + 0.5; */ - fadd fp5,fp5,fp13 /* r1 = r1 + TWO52; */ - fsub fp5,fp5,fp13 /* r1 = r1 - TWO52; */ - b .L9 -.L6: /* if (x < 0.0) */ - fctidz fp0,fp8 - fcfid fp8,fp0 /* tau = floor(x_high/TWO52); */ - bnl cr5,.L7 /* if (x_low < 0.0) */ - fmr fp3,fp1 - fmr fp4,fp2 - b .L8 -.L7: /* if (x_low > 0.0) */ - fsub fp3,fp1,fp8 /* x0 = x_high - tau; */ - fadd fp4,fp2,fp8 /* x1 = x_low + tau; */ -.L8: - fsub fp5,fp4,fp10 /* r1 = x1 - 0.5; */ - fsub fp5,fp5,fp13 /* r1-= TWO52; */ - fadd fp5,fp5,fp13 /* r1+= TWO52; */ -.L9: - mtfsf 0x01,fp11 /* restore previous rounding mode. */ - fadd fp1,fp3,fp5 /* y_high = x0 + r1; */ - fsub fp2,fp3,fp1 /* y_low = x0 - y_high + r1; */ - fadd fp2,fp2,fp5 - blr -END (__roundl) - -long_double_symbol (libm, __roundl, roundl)