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  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.       /*
  79.        * Clamp to max finite value if overflowed.
  80.        * OpenGL has completely undefined rounding behavior for float to
  81.        * half-float conversions, and this matches what is mandated for float
  82.        * to fp11/fp10, which recommend round-to-nearest-finite too.
  83.        * (d3d10 is deeply unhappy about flushing such values to infinity, and
  84.        * while it also mandates round-to-zero it doesn't care nearly as much
  85.        * about that.)
  86.        */
  87.       if (f32.ui > f16inf)
  88.          f32.ui = f16inf - 1;
  89.  
  90.       f16 = f32.ui >> 13;
  91.    }
  92.  
  93.    /* Sign */
  94.    f16 |= sign >> 16;
  95.  
  96.    return f16;
  97. }
  98.  
  99. static INLINE float
  100. util_half_to_float(uint16_t f16)
  101. {
  102.    union fi infnan;
  103.    union fi magic;
  104.    union fi f32;
  105.  
  106.    infnan.ui = 0x8f << 23;
  107.    infnan.f = 65536.0f;
  108.    magic.ui  = 0xef << 23;
  109.  
  110.    /* Exponent / Mantissa */
  111.    f32.ui = (f16 & 0x7fff) << 13;
  112.  
  113.    /* Adjust */
  114.    f32.f *= magic.f;
  115.  
  116.    /* Inf / NaN */
  117.    if (f32.f >= infnan.f)
  118.       f32.ui |= 0xff << 23;
  119.  
  120.    /* Sign */
  121.    f32.ui |= (f16 & 0x8000) << 16;
  122.  
  123.    return f32.f;
  124. }
  125.  
  126. #ifdef __cplusplus
  127. }
  128. #endif
  129.  
  130. #endif /* U_HALF_H */
  131.  
  132.