Mesa (master): Remove _mesa_inv_sqrtf in favor of 1/SQRTF
Matt Turner
mattst88 at kemper.freedesktop.org
Sat Jul 21 15:22:54 UTC 2012
Module: Mesa
Branch: master
Commit: f58ba6ca9147137c7a2d31a1014235f7077b7752
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=f58ba6ca9147137c7a2d31a1014235f7077b7752
Author: Matt Turner <mattst88 at gmail.com>
Date: Fri Jul 20 10:06:35 2012 -0700
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 <brianp at vmware.com>
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
---
src/mesa/main/imports.c | 106 --------------------------------------------
src/mesa/main/imports.h | 9 +---
src/mesa/tnl/t_rasterpos.c | 2 +-
src/mesa/tnl/t_vb_texgen.c | 4 +-
4 files changed, 4 insertions(+), 117 deletions(-)
diff --git a/src/mesa/main/imports.c b/src/mesa/main/imports.c
index fc30a6e..e7e877b 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 e825f21..2544400 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
diff --git a/src/mesa/tnl/t_rasterpos.c b/src/mesa/tnl/t_rasterpos.c
index 50b5fcb..a28ad0d 100644
--- a/src/mesa/tnl/t_rasterpos.c
+++ b/src/mesa/tnl/t_rasterpos.c
@@ -271,7 +271,7 @@ compute_texgen(struct gl_context *ctx, const GLfloat vObj[4], const GLfloat vEye
rz = u[2] - normal[2] * two_nu;
m = rx * rx + ry * ry + (rz + 1.0F) * (rz + 1.0F);
if (m > 0.0F)
- mInv = 0.5F * _mesa_inv_sqrtf(m);
+ mInv = 0.5F * INV_SQRTF(m);
else
mInv = 0.0F;
diff --git a/src/mesa/tnl/t_vb_texgen.c b/src/mesa/tnl/t_vb_texgen.c
index 61430c3..d4c7885 100644
--- a/src/mesa/tnl/t_vb_texgen.c
+++ b/src/mesa/tnl/t_vb_texgen.c
@@ -117,7 +117,7 @@ static void build_m3( GLfloat f[][3], GLfloat m[],
fz = f[i][2] = u[2] - norm[2] * two_nu;
m[i] = fx * fx + fy * fy + (fz + 1.0F) * (fz + 1.0F);
if (m[i] != 0.0F) {
- m[i] = 0.5F * _mesa_inv_sqrtf(m[i]);
+ m[i] = 0.5F * INV_SQRTF(m[i]);
}
}
}
@@ -146,7 +146,7 @@ static void build_m2( GLfloat f[][3], GLfloat m[],
fz = f[i][2] = u[2] - norm[2] * two_nu;
m[i] = fx * fx + fy * fy + (fz + 1.0F) * (fz + 1.0F);
if (m[i] != 0.0F) {
- m[i] = 0.5F * _mesa_inv_sqrtf(m[i]);
+ m[i] = 0.5F * INV_SQRTF(m[i]);
}
}
}
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