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