/* $XFree86: xc/extras/Mesa/src/mmath.c,v 1.8 2003/10/22 15:27:40 tsi 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. */ #include "glheader.h" #include "mmath.h" /* * 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 = _mesa_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) _mesa_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; #if defined(_FPU_GETCW) && defined(_FPU_SETCW) { const char *debug = _mesa_getenv("MESA_DEBUG"); if (debug && _mesa_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; }