diff options
author | Matt Turner <[email protected]> | 2012-07-20 10:06:35 -0700 |
---|---|---|
committer | Matt Turner <[email protected]> | 2012-07-21 08:23:38 -0700 |
commit | f58ba6ca9147137c7a2d31a1014235f7077b7752 (patch) | |
tree | 46f6d2c75436d591cfd66721fd00de8301373437 /src/mesa/main | |
parent | 948b1c541f32b12e8264b1eeb79ccbb696661f54 (diff) |
Remove _mesa_inv_sqrtf in favor of 1/SQRTF
Except for a couple of explicit uses, _mesa_inv_sqrtf was disabled since
its addition in 2003 (see f9b1e524).
Reviewed-by: Brian Paul <[email protected]>
Reviewed-by: Kenneth Graunke <[email protected]>
Diffstat (limited to 'src/mesa/main')
-rw-r--r-- | src/mesa/main/imports.c | 106 | ||||
-rw-r--r-- | src/mesa/main/imports.h | 9 |
2 files changed, 1 insertions, 114 deletions
diff --git a/src/mesa/main/imports.c b/src/mesa/main/imports.c index fc30a6eb671..e7e877be002 100644 --- a/src/mesa/main/imports.c +++ b/src/mesa/main/imports.c @@ -244,112 +244,6 @@ _mesa_memset16( unsigned short *dst, unsigned short val, size_t n ) /*@{*/ -/** - inv_sqrt - A single precision 1/sqrt routine for IEEE format floats. - written by Josh Vanderhoof, based on newsgroup posts by James Van Buskirk - and Vesa Karvonen. -*/ -float -_mesa_inv_sqrtf(float n) -{ -#if defined(USE_IEEE) && !defined(DEBUG) - float r0, x0, y0; - float r1, x1, y1; - float r2, x2, y2; -#if 0 /* not used, see below -BP */ - float r3, x3, y3; -#endif - fi_type u; - unsigned int magic; - - /* - Exponent part of the magic number - - - We want to: - 1. subtract the bias from the exponent, - 2. negate it - 3. divide by two (rounding towards -inf) - 4. add the bias back - - Which is the same as subtracting the exponent from 381 and dividing - by 2. - - floor(-(x - 127) / 2) + 127 = floor((381 - x) / 2) - */ - - magic = 381 << 23; - - /* - Significand part of magic number - - - With the current magic number, "(magic - u.i) >> 1" will give you: - - for 1 <= u.f <= 2: 1.25 - u.f / 4 - for 2 <= u.f <= 4: 1.00 - u.f / 8 - - This isn't a bad approximation of 1/sqrt. The maximum difference from - 1/sqrt will be around .06. After three Newton-Raphson iterations, the - maximum difference is less than 4.5e-8. (Which is actually close - enough to make the following bias academic...) - - To get a better approximation you can add a bias to the magic - number. For example, if you subtract 1/2 of the maximum difference in - the first approximation (.03), you will get the following function: - - for 1 <= u.f <= 2: 1.22 - u.f / 4 - for 2 <= u.f <= 3.76: 0.97 - u.f / 8 - for 3.76 <= u.f <= 4: 0.72 - u.f / 16 - (The 3.76 to 4 range is where the result is < .5.) - - This is the closest possible initial approximation, but with a maximum - error of 8e-11 after three NR iterations, it is still not perfect. If - you subtract 0.0332281 instead of .03, the maximum error will be - 2.5e-11 after three NR iterations, which should be about as close as - is possible. - - for 1 <= u.f <= 2: 1.2167719 - u.f / 4 - for 2 <= u.f <= 3.73: 0.9667719 - u.f / 8 - for 3.73 <= u.f <= 4: 0.7167719 - u.f / 16 - - */ - - magic -= (int)(0.0332281 * (1 << 25)); - - u.f = n; - u.i = (magic - u.i) >> 1; - - /* - Instead of Newton-Raphson, we use Goldschmidt's algorithm, which - allows more parallelism. From what I understand, the parallelism - comes at the cost of less precision, because it lets error - accumulate across iterations. - */ - x0 = 1.0f; - y0 = 0.5f * n; - r0 = u.f; - - x1 = x0 * r0; - y1 = y0 * r0 * r0; - r1 = 1.5f - y1; - - x2 = x1 * r1; - y2 = y1 * r1 * r1; - r2 = 1.5f - y2; - -#if 1 - return x2 * r2; /* we can stop here, and be conformant -BP */ -#else - x3 = x2 * r2; - y3 = y2 * r2 * r2; - r3 = 1.5f - y3; - - return x3 * r3; -#endif -#else - return (float) (1.0 / sqrt(n)); -#endif -} - #ifndef __GNUC__ /** * Find the first bit set in a word. diff --git a/src/mesa/main/imports.h b/src/mesa/main/imports.h index e825f21801b..254440093c5 100644 --- a/src/mesa/main/imports.h +++ b/src/mesa/main/imports.h @@ -105,11 +105,7 @@ typedef union { GLfloat f; GLint i; } fi_type; /*** *** INV_SQRTF: single-precision inverse square root ***/ -#if 0 -#define INV_SQRTF(X) _mesa_inv_sqrt(X) -#else -#define INV_SQRTF(X) (1.0F / SQRTF(X)) /* this is faster on a P4 */ -#endif +#define INV_SQRTF(X) (1.0F / SQRTF(X)) /** @@ -565,9 +561,6 @@ _mesa_realloc( void *oldBuffer, size_t oldSize, size_t newSize ); extern void _mesa_memset16( unsigned short *dst, unsigned short val, size_t n ); -extern float -_mesa_inv_sqrtf(float x); - #ifndef FFS_DEFINED #define FFS_DEFINED 1 |