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/* $Id: mmath.c,v 1.1 2003-02-28 11:42:03 pj Exp $ */
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/*
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 * Mesa 3-D graphics library
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 * Version:  3.5
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 *
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 * Copyright (C) 1999-2001  Brian Paul   All Rights Reserved.
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 *
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 * Permission is hereby granted, free of charge, to any person obtaining a
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 * copy of this software and associated documentation files (the "Software"),
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 * to deal in the Software without restriction, including without limitation
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 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
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 * and/or sell copies of the Software, and to permit persons to whom the
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 * Software is furnished to do so, subject to the following conditions:
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 *
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 * The above copyright notice and this permission notice shall be included
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 * in all copies or substantial portions of the Software.
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 *
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 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
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 * BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
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 * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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 */
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#include "glheader.h"
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#include "mmath.h"
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static int in_fast_math;
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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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   fi_type fi;     /* to access the bits of a float in  C quickly  */
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                   /* we use a union defined in glheader.h         */
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   for(i=0; i<= 0x7f; i++) {
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      fi.i = 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 = (i << 16) | (127 << 23);
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      fi.f = _mesa_sqrt(fi.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.i & 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.i = 0;
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      fi.i = (i << 16) | (128 << 23);
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      fi.f = sqrt(fi.f);
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      sqrttab[i+0x80] = (fi.i & 0x7fffff) >> 16;
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   }
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#else
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   (void) sqrttab;  /* silence compiler warnings */
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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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   fi_type num;
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                                /* to access the bits of a float in C
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                                 * we use a union from glheader.h     */
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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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   num.f = x;
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   e = (num.i >> 23) - 127;     /* get the exponent - on a SPARC the */
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                                /* exponent is stored with 127 added */
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   num.i &= 0x7fffff;           /* leave only the mantissa */
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   if (e & 0x01) num.i |= 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.i = ((sqrttab[num.i >> 16]) << 16) | ((e + 127) << 23);
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   return num.f;
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#else
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   return (GLfloat) _mesa_sqrt(x);
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#endif
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}
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/* ubyte -> float conversion */
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float _mesa_ubyte_to_float_color_tab[256];
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/*
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 * Initialize tables, etc for fast math functions.
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 */
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void
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_mesa_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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      int i;
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      for (i = 0; i < 256; i++) {
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         _mesa_ubyte_to_float_color_tab[i] = (float) i / 255.0F;
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      }
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      init_sqrt();
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      initialized = GL_TRUE;
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      in_fast_math = 0;
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#if defined(_FPU_GETCW) && defined(_FPU_SETCW)
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      {
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         const char *debug = _mesa_getenv("MESA_DEBUG");
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         if (debug && _mesa_strcmp(debug, "FP")==0) {
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            /* die on FP exceptions */
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            fpu_control_t mask;
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            _FPU_GETCW(mask);
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            mask &= ~(_FPU_MASK_IM | _FPU_MASK_DM | _FPU_MASK_ZM
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                      | _FPU_MASK_OM | _FPU_MASK_UM);
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            _FPU_SETCW(mask);
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         }
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      }
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#endif
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   }
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}
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/*
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 * Return number of bits set in given GLuint.
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 */
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GLuint
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_mesa_bitcount(GLuint n)
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{
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   GLuint bits;
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   for (bits = 0; n > 0; n = n >> 1) {
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      if (n & 1) {
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         bits++;
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      }
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   }
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   return bits;
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}