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Correct vec_perm() application on little-endian 64-bit PowerPC
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The LE transformation for vec_perm has an implicit assumption that the
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permutation is being used to reorder vector elements (in this case 4-byte
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integer word elements), not to reorder bytes within those elements. Although
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this is legal behavior, it is not anticipated by the transformation performed
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by the compilers.
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This causes pygame-1.9.1 test failure on PPC64LE because blitted pixmaps are
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corrupted there due to how SDL uses vec_perm().
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<https://bugzilla.redhat.com/show_bug.cgi?id=1392465>
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--- SDL-1.2.15/src/video/SDL_blit_N.c.ori 2017-09-04 05:56:17.759347525 -0400
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+++ SDL-1.2.15/src/video/SDL_blit_N.c 2017-09-06 05:36:20.570789610 -0400
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@@ -146,6 +146,32 @@ static vector unsigned char calc_swizzle
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return(vswiz);
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}
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+/* reorder bytes for PowerPC little endian */
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+static vector unsigned char reorder_ppc64le_vec(vector unsigned char vpermute)
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+{
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+ /* The result vector of calc_swizzle32 reorder bytes using vec_perm.
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+ The LE transformation for vec_perm has an implicit assumption
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+ that the permutation is being used to reorder vector elements,
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+ not to reorder bytes within those elements.
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+ Unfortunatly the result order is not the expected one for powerpc
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+ little endian when the two first vector parameters of vec_perm are
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+ not of type 'vector char'. This is because the numbering from the
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+ left for BE, and numbering from the right for LE, produces a
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+ different interpretation of what the odd and even lanes are.
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+ Refer to fedora bug 1392465
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+ */
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+
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+ const vector unsigned char ppc64le_reorder = VECUINT8_LITERAL(
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+ 0x01, 0x00, 0x03, 0x02,
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+ 0x05, 0x04, 0x07, 0x06,
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+ 0x09, 0x08, 0x0B, 0x0A,
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+ 0x0D, 0x0C, 0x0F, 0x0E );
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+
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+ vector unsigned char vswiz_ppc64le;
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+ vswiz_ppc64le = vec_perm(vpermute, vpermute, ppc64le_reorder);
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+ return(vswiz_ppc64le);
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+}
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+
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static void Blit_RGB888_RGB565(SDL_BlitInfo *info);
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static void Blit_RGB888_RGB565Altivec(SDL_BlitInfo *info) {
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int height = info->d_height;
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@@ -631,6 +657,12 @@ static void Blit32to32KeyAltivec(SDL_Bli
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vsel = (vector unsigned char)vec_and(vs, vrgbmask);
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vsel = (vector unsigned char)vec_cmpeq(vs, vckey);
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/* permute the src vec to the dest format */
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+
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+#if defined(__powerpc__) && (SDL_BYTEORDER == SDL_LIL_ENDIAN)
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+ /* reorder bytes for PowerPC little endian */
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+ vpermute = reorder_ppc64le_vec(vpermute);
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+#endif
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+
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vs = vec_perm(vs, valpha, vpermute);
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/* load the destination vec */
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vd = vec_ld(0, dstp);
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@@ -704,6 +736,12 @@ static void ConvertAltivec32to32_noprefe
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src += 4;
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width -= 4;
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vbits = vec_perm(vbits, voverflow, valigner); /* src is ready. */
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+
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+#if defined(__powerpc__) && (SDL_BYTEORDER == SDL_LIL_ENDIAN)
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+ /* reorder bytes for PowerPC little endian */
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+ vpermute = reorder_ppc64le_vec(vpermute);
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+#endif
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+
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vbits = vec_perm(vbits, vzero, vpermute); /* swizzle it. */
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vec_st(vbits, 0, dst); /* store it back out. */
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dst += 4;
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@@ -786,6 +824,12 @@ static void ConvertAltivec32to32_prefetc
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src += 4;
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width -= 4;
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vbits = vec_perm(vbits, voverflow, valigner); /* src is ready. */
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+
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+#if defined(__powerpc__) && (SDL_BYTEORDER == SDL_LIL_ENDIAN)
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+ /* reorder bytes for PowerPC little endian */
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+ vpermute = reorder_ppc64le_vec(vpermute);
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+#endif
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+
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vbits = vec_perm(vbits, vzero, vpermute); /* swizzle it. */
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vec_st(vbits, 0, dst); /* store it back out. */
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dst += 4;
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