SDL_blit_N.c: Correct vec_perm() application on little-endian 64-bit PowerPC
The LE transformation for vec_perm has an implicit assumption that the
permutation is being used to reorder vector elements (in this case 4-byte
integer word elements), not to reorder bytes within those elements. Although
this is legal behavior, it is not anticipated by the transformation performed
by the compilers.
This causes pygame-1.9.1 test failure on PPC64LE because blitted pixmaps are
corrupted there due to how SDL uses vec_perm().
From RedHat / Fedora: https://bugzilla.redhat.com/show_bug.cgi?id=1392465
Original patch was provided by: Menanteau Guy <menantea@linux.vnet.ibm.com>
diff --git a/src/video/SDL_blit_N.c b/src/video/SDL_blit_N.c
index 2460a79..59e2fdb 100644
--- a/src/video/SDL_blit_N.c
+++ b/src/video/SDL_blit_N.c
@@ -165,6 +165,34 @@
return (vswiz);
}
+#if defined(__powerpc__) && (SDL_BYTEORDER == SDL_LIL_ENDIAN)
+/* reorder bytes for PowerPC little endian */
+static vector unsigned char reorder_ppc64le_vec(vector unsigned char vpermute)
+{
+ /* The result vector of calc_swizzle32 reorder bytes using vec_perm.
+ The LE transformation for vec_perm has an implicit assumption
+ that the permutation is being used to reorder vector elements,
+ not to reorder bytes within those elements.
+ Unfortunatly the result order is not the expected one for powerpc
+ little endian when the two first vector parameters of vec_perm are
+ not of type 'vector char'. This is because the numbering from the
+ left for BE, and numbering from the right for LE, produces a
+ different interpretation of what the odd and even lanes are.
+ Refer to fedora bug 1392465
+ */
+
+ const vector unsigned char ppc64le_reorder = VECUINT8_LITERAL(
+ 0x01, 0x00, 0x03, 0x02,
+ 0x05, 0x04, 0x07, 0x06,
+ 0x09, 0x08, 0x0B, 0x0A,
+ 0x0D, 0x0C, 0x0F, 0x0E );
+
+ vector unsigned char vswiz_ppc64le;
+ vswiz_ppc64le = vec_perm(vpermute, vpermute, ppc64le_reorder);
+ return(vswiz_ppc64le);
+}
+#endif
+
static void Blit_RGB888_RGB565(SDL_BlitInfo * info);
static void
Blit_RGB888_RGB565Altivec(SDL_BlitInfo * info)
@@ -658,6 +686,10 @@
/* vsel is set for items that match the key */
vsel = (vector unsigned char) vec_and(vs, vrgbmask);
vsel = (vector unsigned char) vec_cmpeq(vs, vckey);
+#if defined(__powerpc__) && (SDL_BYTEORDER == SDL_LIL_ENDIAN)
+ /* reorder bytes for PowerPC little endian */
+ vpermute = reorder_ppc64le_vec(vpermute);
+#endif
/* permute the src vec to the dest format */
vs = vec_perm(vs, valpha, vpermute);
/* load the destination vec */
@@ -737,6 +769,10 @@
src += 4;
width -= 4;
vbits = vec_perm(vbits, voverflow, valigner); /* src is ready. */
+#if defined(__powerpc__) && (SDL_BYTEORDER == SDL_LIL_ENDIAN)
+ /* reorder bytes for PowerPC little endian */
+ vpermute = reorder_ppc64le_vec(vpermute);
+#endif
vbits = vec_perm(vbits, vzero, vpermute); /* swizzle it. */
vec_st(vbits, 0, dst); /* store it back out. */
dst += 4;
@@ -828,6 +864,10 @@
src += 4;
width -= 4;
vbits = vec_perm(vbits, voverflow, valigner); /* src is ready. */
+#if defined(__powerpc__) && (SDL_BYTEORDER == SDL_LIL_ENDIAN)
+ /* reorder bytes for PowerPC little endian */
+ vpermute = reorder_ppc64le_vec(vpermute);
+#endif
vbits = vec_perm(vbits, vzero, vpermute); /* swizzle it. */
vec_st(vbits, 0, dst); /* store it back out. */
dst += 4;
