src/gallium/auxiliary/util/u_half.h

   1 /**************************************************************************
   2  *
   3  * Copyright 2010 Luca Barbieri
   4  *
   5  * Permission is hereby granted, free of charge, to any person obtaining
   6  * a copy of this software and associated documentation files (the
   7  * "Software"), to deal in the Software without restriction, including
   8  * without limitation the rights to use, copy, modify, merge, publish,
   9  * distribute, sublicense, and/or sell copies of the Software, and to
  10  * permit persons to whom the Software is furnished to do so, subject to
  11  * the following conditions:
  12  *
  13  * The above copyright notice and this permission notice (including the
  14  * next paragraph) shall be included in all copies or substantial
  15  * portions of the Software.
  16  *
  17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  18  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  19  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
  20  * IN NO EVENT SHALL THE COPYRIGHT OWNER(S) AND/OR ITS SUPPLIERS BE
  21  * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  22  * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  23  * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  24  *
  25  **************************************************************************/
  26
  27
  28 #ifndef U_HALF_H
  29 #define U_HALF_H
  30
  31 #include "pipe/p_compiler.h"
  32 #include "util/u_math.h"
  33
  34 #ifdef __cplusplus
  35 extern "C" {
  36 #endif
  37
  38 /*
  39  * References for float <-> half conversions
  40  *
  41  *  http://fgiesen.wordpress.com/2012/03/28/half-to-float-done-quic/
  42  *  https://gist.github.com/2156668
  43  *  https://gist.github.com/2144712
  44  */
  45
  46 static INLINE uint16_t
  47 util_float_to_half(float f)
  48 {
  49    uint32_t sign_mask  = 0x80000000;
  50    uint32_t round_mask = ~0xfff;
  51    uint32_t f32inf = 0xff << 23;
  52    uint32_t f16inf = 0x1f << 23;
  53    uint32_t sign;
  54    union fi magic;
  55    union fi f32;
  56    uint16_t f16;
  57
  58    magic.ui = 0xf << 23;
  59
  60    f32.f = f;
  61
  62    /* Sign */
  63    sign = f32.ui & sign_mask;
  64    f32.ui ^= sign;
  65
  66    if (f32.ui == f32inf) {
  67       /* Inf */
  68       f16 = 0x7c00;
  69    } else if (f32.ui > f32inf) {
  70       /* NaN */
  71       f16 = 0x7e00;
  72    } else {
  73       /* Number */
  74       f32.ui &= round_mask;
  75       f32.f  *= magic.f;
  76       f32.ui -= round_mask;
  77
  78       /* Clamp to infinity if overflowed */
  79       if (f32.ui > f16inf)
  80          f32.ui = f16inf;
  81
  82       f16 = f32.ui >> 13;
  83    }
  84
  85    /* Sign */
  86    f16 |= sign >> 16;
  87
  88    return f16;
  89 }
  90
  91 static INLINE float
  92 util_half_to_float(uint16_t f16)
  93 {
  94    union fi infnan;
  95    union fi magic;
  96    union fi f32;
  97
  98    infnan.ui = 0x8f << 23;
  99    infnan.f = 65536.0f;
 100    magic.ui  = 0xef << 23;
 101
 102    /* Exponent / Mantissa */
 103    f32.ui = (f16 & 0x7fff) << 13;
 104
 105    /* Adjust */
 106    f32.f *= magic.f;
 107
 108    /* Inf / NaN */
 109    if (f32.f >= infnan.f)
 110       f32.ui |= 0xff << 23;
 111
 112    /* Sign */
 113    f32.ui |= (f16 & 0x8000) << 16;
 114
 115    return f32.f;
 116 }
 117
 118 #ifdef __cplusplus
 119 }
 120 #endif
 121
 122 #endif /* U_HALF_H */
 123