mirror of
https://github.com/reactos/reactos.git
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5f2bebf7a5
With this commit, we now use a forked version of MESA which only supports OpenGL 1.1, like the windows implementation does. It exposes : - The same pixel formats - The same set of extensions - Nothing more All of this without taking 10% of your build time. If you need a more modern option, look at the MESA package from Rapps, which is (and must be) maintained outside of this code tree. CORE-7499
151 lines
4.1 KiB
C
151 lines
4.1 KiB
C
/* $Id: mmath.c,v 1.3 1997/07/24 01:23:16 brianp Exp $ */
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/*
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* Mesa 3-D graphics library
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* Version: 2.4
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* Copyright (C) 1995-1997 Brian Paul
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Library General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Library General Public License for more details.
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*
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* You should have received a copy of the GNU Library General Public
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* License along with this library; if not, write to the Free
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* Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/*
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* $Log: mmath.c,v $
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* Revision 1.3 1997/07/24 01:23:16 brianp
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* changed precompiled header symbol from PCH to PC_HEADER
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*
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* Revision 1.2 1997/05/28 03:25:43 brianp
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* added precompiled header (PCH) support
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*
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* Revision 1.1 1997/05/01 01:41:54 brianp
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* Initial revision
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*
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*/
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#ifdef PC_HEADER
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#include "all.h"
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#else
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#include "GL/gl.h"
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#include "mmath.h"
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#endif
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/*
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* A High Speed, Low Precision Square Root
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* by Paul Lalonde and Robert Dawson
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* from "Graphics Gems", Academic Press, 1990
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*/
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/*
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* SPARC implementation of a fast square root by table
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* lookup.
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* SPARC floating point format is as follows:
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*
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* BIT 31 30 23 22 0
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* sign exponent mantissa
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*/
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static short sqrttab[0x100]; /* declare table of square roots */
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static void init_sqrt(void)
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{
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#ifdef FAST_MATH
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unsigned short i;
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float f;
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unsigned int *fi = (unsigned int *)&f;
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/* to access the bits of a float in */
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/* C quickly we must misuse pointers */
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for(i=0; i<= 0x7f; i++) {
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*fi = 0;
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/*
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* Build a float with the bit pattern i as mantissa
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* and an exponent of 0, stored as 127
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*/
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*fi = (i << 16) | (127 << 23);
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f = sqrt(f);
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/*
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* Take the square root then strip the first 7 bits of
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* the mantissa into the table
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*/
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sqrttab[i] = (*fi & 0x7fffff) >> 16;
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/*
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* Repeat the process, this time with an exponent of
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* 1, stored as 128
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*/
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*fi = 0;
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*fi = (i << 16) | (128 << 23);
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f = sqrt(f);
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sqrttab[i+0x80] = (*fi & 0x7fffff) >> 16;
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}
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#endif /*FAST_MATH*/
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}
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float gl_sqrt( float x )
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{
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#ifdef FAST_MATH
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unsigned int *num = (unsigned int *)&x;
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/* to access the bits of a float in C
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* we must misuse pointers */
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short e; /* the exponent */
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if (x == 0.0F) return 0.0F; /* check for square root of 0 */
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e = (*num >> 23) - 127; /* get the exponent - on a SPARC the */
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/* exponent is stored with 127 added */
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*num &= 0x7fffff; /* leave only the mantissa */
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if (e & 0x01) *num |= 0x800000;
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/* the exponent is odd so we have to */
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/* look it up in the second half of */
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/* the lookup table, so we set the */
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/* high bit */
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e >>= 1; /* divide the exponent by two */
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/* note that in C the shift */
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/* operators are sign preserving */
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/* for signed operands */
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/* Do the table lookup, based on the quaternary mantissa,
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* then reconstruct the result back into a float
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*/
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*num = ((sqrttab[*num >> 16]) << 16) | ((e + 127) << 23);
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return x;
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#else
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return sqrt(x);
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#endif
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}
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/*
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* Initialize tables, etc for fast math functions.
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*/
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void gl_init_math(void)
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{
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static GLboolean initialized = GL_FALSE;
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if (!initialized) {
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init_sqrt();
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initialized = GL_TRUE;
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}
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}
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