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/* $XFree86: xc/extras/Mesa/src/mmath.c,v 1.6 2002/02/22 19:25:36 dawes Exp $ */
/*
* Mesa 3-D graphics library
* Version: 3.5
*
* Copyright (C) 1999-2001 Brian Paul All Rights Reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included
* in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
* AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#ifdef PC_HEADER
#include "all.h"
#else
#include "glheader.h"
#include "mmath.h"
#endif
static int in_fast_math;
/*
* A High Speed, Low Precision Square Root
* by Paul Lalonde and Robert Dawson
* from "Graphics Gems", Academic Press, 1990
*/
/*
* SPARC implementation of a fast square root by table
* lookup.
* SPARC floating point format is as follows:
*
* BIT 31 30 23 22 0
* sign exponent mantissa
*/
static short sqrttab[0x100]; /* declare table of square roots */
static void init_sqrt(void)
{
#ifdef FAST_MATH
unsigned short i;
fi_type fi; /* to access the bits of a float in C quickly */
/* we use a union defined in glheader.h */
for(i=0; i<= 0x7f; i++) {
fi.i = 0;
/*
* Build a float with the bit pattern i as mantissa
* and an exponent of 0, stored as 127
*/
fi.i = (i << 16) | (127 << 23);
fi.f = sqrt(fi.f);
/*
* Take the square root then strip the first 7 bits of
* the mantissa into the table
*/
sqrttab[i] = (fi.i & 0x7fffff) >> 16;
/*
* Repeat the process, this time with an exponent of
* 1, stored as 128
*/
fi.i = 0;
fi.i = (i << 16) | (128 << 23);
fi.f = sqrt(fi.f);
sqrttab[i+0x80] = (fi.i & 0x7fffff) >> 16;
}
#else
(void) sqrttab; /* silence compiler warnings */
#endif /*FAST_MATH*/
}
float gl_sqrt( float x )
{
#ifdef FAST_MATH
fi_type num;
/* to access the bits of a float in C
* we use a union from glheader.h */
short e; /* the exponent */
if (x == 0.0F) return 0.0F; /* check for square root of 0 */
num.f = x;
e = (num.i >> 23) - 127; /* get the exponent - on a SPARC the */
/* exponent is stored with 127 added */
num.i &= 0x7fffff; /* leave only the mantissa */
if (e & 0x01) num.i |= 0x800000;
/* the exponent is odd so we have to */
/* look it up in the second half of */
/* the lookup table, so we set the */
/* high bit */
e >>= 1; /* divide the exponent by two */
/* note that in C the shift */
/* operators are sign preserving */
/* for signed operands */
/* Do the table lookup, based on the quaternary mantissa,
* then reconstruct the result back into a float
*/
num.i = ((sqrttab[num.i >> 16]) << 16) | ((e + 127) << 23);
return num.f;
#else
return (GLfloat) sqrt(x);
#endif
}
/* ubyte -> float conversion */
float _mesa_ubyte_to_float_color_tab[256];
/*
* Initialize tables, etc for fast math functions.
*/
void
_mesa_init_math(void)
{
static GLboolean initialized = GL_FALSE;
if (!initialized) {
int i;
for (i = 0; i < 256; i++) {
_mesa_ubyte_to_float_color_tab[i] = (float) i / 255.0F;
}
init_sqrt();
initialized = GL_TRUE;
in_fast_math = 0;
#if defined(_FPU_GETCW) && defined(_FPU_SETCW)
{
const char *debug = getenv("MESA_DEBUG");
if (debug && strcmp(debug, "FP")==0) {
/* die on FP exceptions */
fpu_control_t mask;
_FPU_GETCW(mask);
mask &= ~(_FPU_MASK_IM | _FPU_MASK_DM | _FPU_MASK_ZM
| _FPU_MASK_OM | _FPU_MASK_UM);
_FPU_SETCW(mask);
}
}
#endif
}
}
/*
* Return number of bits set in given GLuint.
*/
GLuint
_mesa_bitcount(GLuint n)
{
GLuint bits;
for (bits = 0; n > 0; n = n >> 1) {
if (n & 1) {
bits++;
}
}
return bits;
}
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