1 /* 2 * Copyright (C) 2011 Marek Olk <maraeo (at) gmail.com> 3 * 4 * Permission is hereby granted, free of charge, to any person obtaining a 5 * copy of this software and associated documentation files (the "Software"), 6 * to deal in the Software without restriction, including without limitation 7 * the rights to use, copy, modify, merge, publish, distribute, sublicense, 8 * and/or sell copies of the Software, and to permit persons to whom the 9 * Software is furnished to do so, subject to the following conditions: 10 * 11 * The above copyright notice and this permission notice (including the next 12 * paragraph) shall be included in all copies or substantial portions of the 13 * Software. 14 * 15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 21 * DEALINGS IN THE SOFTWARE. 22 */ 23 24 /* Copied from EXT_texture_shared_exponent and edited, getting rid of 25 * expensive float math bits too. */ 26 27 #ifndef RGB9E5_H 28 #define RGB9E5_H 29 30 #include <assert.h> 31 #include <stdint.h> 32 33 #include "c99_math.h" 34 35 #define RGB9E5_EXPONENT_BITS 5 36 #define RGB9E5_MANTISSA_BITS 9 37 #define RGB9E5_EXP_BIAS 15 38 #define RGB9E5_MAX_VALID_BIASED_EXP 31 39 40 #define MAX_RGB9E5_EXP (RGB9E5_MAX_VALID_BIASED_EXP - RGB9E5_EXP_BIAS) 41 #define RGB9E5_MANTISSA_VALUES (1<<RGB9E5_MANTISSA_BITS) 42 #define MAX_RGB9E5_MANTISSA (RGB9E5_MANTISSA_VALUES-1) 43 #define MAX_RGB9E5 (((float)MAX_RGB9E5_MANTISSA)/RGB9E5_MANTISSA_VALUES * (1<<MAX_RGB9E5_EXP)) 44 45 static inline int rgb9e5_ClampRange(float x) 46 { 47 union { float f; uint32_t u; } f, max; 48 f.f = x; 49 max.f = MAX_RGB9E5; 50 51 if (f.u > 0x7f800000) 52 /* catches neg, NaNs */ 53 return 0; 54 else if (f.u >= max.u) 55 return max.u; 56 else 57 return f.u; 58 } 59 60 static inline uint32_t float3_to_rgb9e5(const float rgb[3]) 61 { 62 int rm, gm, bm, exp_shared; 63 uint32_t revdenom_biasedexp; 64 union { float f; uint32_t u; } rc, bc, gc, maxrgb, revdenom; 65 66 rc.u = rgb9e5_ClampRange(rgb[0]); 67 gc.u = rgb9e5_ClampRange(rgb[1]); 68 bc.u = rgb9e5_ClampRange(rgb[2]); 69 maxrgb.u = MAX3(rc.u, gc.u, bc.u); 70 71 /* 72 * Compared to what the spec suggests, instead of conditionally adjusting 73 * the exponent after the fact do it here by doing the equivalent of +0.5 - 74 * the int add will spill over into the exponent in this case. 75 */ 76 maxrgb.u += maxrgb.u & (1 << (23-9)); 77 exp_shared = MAX2((maxrgb.u >> 23), -RGB9E5_EXP_BIAS - 1 + 127) + 78 1 + RGB9E5_EXP_BIAS - 127; 79 revdenom_biasedexp = 127 - (exp_shared - RGB9E5_EXP_BIAS - 80 RGB9E5_MANTISSA_BITS) + 1; 81 revdenom.u = revdenom_biasedexp << 23; 82 assert(exp_shared <= RGB9E5_MAX_VALID_BIASED_EXP); 83 84 /* 85 * The spec uses strict round-up behavior (d3d10 disagrees, but in any case 86 * must match what is done above for figuring out exponent). 87 * We avoid the doubles ((int) rc * revdenom + 0.5) by doing the rounding 88 * ourselves (revdenom was adjusted by +1, above). 89 */ 90 rm = (int) (rc.f * revdenom.f); 91 gm = (int) (gc.f * revdenom.f); 92 bm = (int) (bc.f * revdenom.f); 93 rm = (rm & 1) + (rm >> 1); 94 gm = (gm & 1) + (gm >> 1); 95 bm = (bm & 1) + (bm >> 1); 96 97 assert(rm <= MAX_RGB9E5_MANTISSA); 98 assert(gm <= MAX_RGB9E5_MANTISSA); 99 assert(bm <= MAX_RGB9E5_MANTISSA); 100 assert(rm >= 0); 101 assert(gm >= 0); 102 assert(bm >= 0); 103 104 return (exp_shared << 27) | (bm << 18) | (gm << 9) | rm; 105 } 106 107 static inline void rgb9e5_to_float3(uint32_t rgb, float retval[3]) 108 { 109 int exponent; 110 union { float f; uint32_t u; } scale; 111 112 exponent = (rgb >> 27) - RGB9E5_EXP_BIAS - RGB9E5_MANTISSA_BITS; 113 scale.u = (exponent + 127) << 23; 114 115 retval[0] = ( rgb & 0x1ff) * scale.f; 116 retval[1] = ((rgb >> 9) & 0x1ff) * scale.f; 117 retval[2] = ((rgb >> 18) & 0x1ff) * scale.f; 118 } 119 120 #endif 121
