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mesa: use __builtin_clz for logbase2 when available

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Also rename to _mesa_logbase2 and move to imports.h to keep the ugly
ifdef GNUC stuff outside other files (also to allow reuse).
This commit is contained in:
Roland Scheidegger 2011-06-09 00:44:32 +02:00
parent b3d5822e93
commit b537f54b3a
2 changed files with 24 additions and 20 deletions
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21
src/mesa/main/imports.h
View file

@ -486,6 +486,27 @@ _mesa_next_pow_two_64(uint64_t x)
}
/*
* Returns the floor form of binary logarithm for a 32-bit integer.
*/
static INLINE GLuint
_mesa_logbase2(GLuint n)
{
#if defined(__GNUC__) && \
((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4)
return (31 - __builtin_clz(n | 1));
#else
GLuint pos = 0;
if (n >= 1<<16) { n >>= 16; pos += 16; }
if (n >= 1<< 8) { n >>= 8; pos += 8; }
if (n >= 1<< 4) { n >>= 4; pos += 4; }
if (n >= 1<< 2) { n >>= 2; pos += 2; }
if (n >= 1<< 1) { pos += 1; }
return pos;
#endif
}
/**
* Return 1 if this is a little endian machine, 0 if big endian.
*/

23
src/mesa/main/teximage.c
View file

@ -80,23 +80,6 @@ _mesa_free_texmemory(void *m)
}
/*
* Returns the floor form of binary logarithm for a 32-bit integer.
*/
static GLuint
logbase2(GLuint n)
{
GLuint pos = 0;
if (n >= 1<<16) { n >>= 16; pos += 16; }
if (n >= 1<< 8) { n >>= 8; pos += 8; }
if (n >= 1<< 4) { n >>= 4; pos += 4; }
if (n >= 1<< 2) { n >>= 2; pos += 2; }
if (n >= 1<< 1) { pos += 1; }
return pos;
}
/**
* Return the simple base format for a given internal texture format.
* For example, given GL_LUMINANCE12_ALPHA4, return GL_LUMINANCE_ALPHA.
@ -1155,7 +1138,7 @@ _mesa_init_teximage_fields(struct gl_context *ctx, GLenum target,
img->Depth = depth;
img->Width2 = width - 2 * border; /* == 1 << img->WidthLog2; */
img->WidthLog2 = logbase2(img->Width2);
img->WidthLog2 = _mesa_logbase2(img->Width2);
if (height == 1) { /* 1-D texture */
img->Height2 = 1;
@ -1163,7 +1146,7 @@ _mesa_init_teximage_fields(struct gl_context *ctx, GLenum target,
}
else {
img->Height2 = height - 2 * border; /* == 1 << img->HeightLog2; */
img->HeightLog2 = logbase2(img->Height2);
img->HeightLog2 = _mesa_logbase2(img->Height2);
}
if (depth == 1) { /* 2-D texture */
@ -1172,7 +1155,7 @@ _mesa_init_teximage_fields(struct gl_context *ctx, GLenum target,
}
else {
img->Depth2 = depth - 2 * border; /* == 1 << img->DepthLog2; */
img->DepthLog2 = logbase2(img->Depth2);
img->DepthLog2 = _mesa_logbase2(img->Depth2);
}
img->MaxLog2 = MAX2(img->WidthLog2, img->HeightLog2);