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| 1 /* | |
| 2 * Copyright 2011 Google Inc. | |
| 3 * | |
| 4 * Use of this source code is governed by a BSD-style license that can be | |
| 5 * found in the LICENSE file. | |
| 6 */ | |
| 7 | |
| 8 #include "SkFloatBits.h" | |
| 9 #include "SkMathPriv.h" | |
| 10 | |
| 11 /****************************************************************************** | |
| 12 SkFloatBits_toInt[Floor, Round, Ceil] are identical except for what they | |
| 13 do right before they return ... >> exp; | |
| 14 Floor - adds nothing | |
| 15 Round - adds 1 << (exp - 1) | |
| 16 Ceil - adds (1 << exp) - 1 | |
| 17 | |
| 18 Floor and Cast are very similar, but Cast applies its sign after all other | |
| 19 computations on value. Also, Cast does not need to check for negative zero, | |
| 20 as that value (0x80000000) "does the right thing" for Ceil. Note that it | |
| 21 doesn't for Floor/Round/Ceil, hence the explicit check. | |
| 22 ******************************************************************************/ | |
| 23 | |
| 24 #define EXP_BIAS (127+23) | |
| 25 #define MATISSA_MAGIC_BIG (1 << 23) | |
| 26 | |
| 27 static inline int unpack_exp(uint32_t packed) { | |
| 28 return (packed << 1 >> 24); | |
| 29 } | |
| 30 | |
| 31 #if 0 | |
| 32 // the ARM compiler generates an extra BIC, so I use the dirty version instead | |
| 33 static inline int unpack_matissa(uint32_t packed) { | |
| 34 // we could mask with 0x7FFFFF, but that is harder for ARM to encode | |
| 35 return (packed & ~0xFF000000) | MATISSA_MAGIC_BIG; | |
| 36 } | |
| 37 #endif | |
| 38 | |
| 39 // returns the low 24-bits, so we need to OR in the magic_bit afterwards | |
| 40 static inline int unpack_matissa_dirty(uint32_t packed) { | |
| 41 return packed & ~0xFF000000; | |
| 42 } | |
| 43 | |
| 44 // same as (int)float | |
| 45 int32_t SkFloatBits_toIntCast(int32_t packed) { | |
| 46 int exp = unpack_exp(packed) - EXP_BIAS; | |
| 47 int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG; | |
| 48 | |
| 49 if (exp >= 0) { | |
| 50 if (exp > 7) { // overflow | |
| 51 value = SK_MaxS32; | |
| 52 } else { | |
| 53 value <<= exp; | |
| 54 } | |
| 55 } else { | |
| 56 exp = -exp; | |
| 57 if (exp > 25) { // underflow | |
| 58 exp = 25; | |
| 59 } | |
| 60 value >>= exp; | |
| 61 } | |
| 62 return SkApplySign(value, SkExtractSign(packed)); | |
| 63 } | |
| 64 | |
| 65 // same as (int)floor(float) | |
| 66 int32_t SkFloatBits_toIntFloor(int32_t packed) { | |
| 67 // curse you negative 0 | |
| 68 if (SkLeftShift(packed, 1) == 0) { | |
| 69 return 0; | |
| 70 } | |
| 71 | |
| 72 int exp = unpack_exp(packed) - EXP_BIAS; | |
| 73 int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG; | |
| 74 | |
| 75 if (exp >= 0) { | |
| 76 if (exp > 7) { // overflow | |
| 77 value = SK_MaxS32; | |
| 78 } else { | |
| 79 value <<= exp; | |
| 80 } | |
| 81 // apply the sign after we check for overflow | |
| 82 return SkApplySign(value, SkExtractSign(packed)); | |
| 83 } else { | |
| 84 // apply the sign before we right-shift | |
| 85 value = SkApplySign(value, SkExtractSign(packed)); | |
| 86 exp = -exp; | |
| 87 if (exp > 25) { // underflow | |
| 88 #ifdef SK_CPU_FLUSH_TO_ZERO | |
| 89 // The iOS ARM processor discards small denormalized numbers to go faste
r. | |
| 90 // The comparision below empirically causes the result to agree with the | |
| 91 // tests in MathTest test_float_floor | |
| 92 if (exp > 149) { | |
| 93 return 0; | |
| 94 } | |
| 95 #else | |
| 96 exp = 25; | |
| 97 #endif | |
| 98 } | |
| 99 // int add = 0; | |
| 100 return value >> exp; | |
| 101 } | |
| 102 } | |
| 103 | |
| 104 // same as (int)floor(float + 0.5) | |
| 105 int32_t SkFloatBits_toIntRound(int32_t packed) { | |
| 106 // curse you negative 0 | |
| 107 if (SkLeftShift(packed, 1) == 0) { | |
| 108 return 0; | |
| 109 } | |
| 110 | |
| 111 int exp = unpack_exp(packed) - EXP_BIAS; | |
| 112 int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG; | |
| 113 | |
| 114 if (exp >= 0) { | |
| 115 if (exp > 7) { // overflow | |
| 116 value = SK_MaxS32; | |
| 117 } else { | |
| 118 value <<= exp; | |
| 119 } | |
| 120 // apply the sign after we check for overflow | |
| 121 return SkApplySign(value, SkExtractSign(packed)); | |
| 122 } else { | |
| 123 // apply the sign before we right-shift | |
| 124 value = SkApplySign(value, SkExtractSign(packed)); | |
| 125 exp = -exp; | |
| 126 if (exp > 25) { // underflow | |
| 127 exp = 25; | |
| 128 } | |
| 129 int add = 1 << (exp - 1); | |
| 130 return (value + add) >> exp; | |
| 131 } | |
| 132 } | |
| 133 | |
| 134 // same as (int)ceil(float) | |
| 135 int32_t SkFloatBits_toIntCeil(int32_t packed) { | |
| 136 // curse you negative 0 | |
| 137 if (SkLeftShift(packed, 1) == 0) { | |
| 138 return 0; | |
| 139 } | |
| 140 | |
| 141 int exp = unpack_exp(packed) - EXP_BIAS; | |
| 142 int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG; | |
| 143 | |
| 144 if (exp >= 0) { | |
| 145 if (exp > 7) { // overflow | |
| 146 value = SK_MaxS32; | |
| 147 } else { | |
| 148 value <<= exp; | |
| 149 } | |
| 150 // apply the sign after we check for overflow | |
| 151 return SkApplySign(value, SkExtractSign(packed)); | |
| 152 } else { | |
| 153 // apply the sign before we right-shift | |
| 154 value = SkApplySign(value, SkExtractSign(packed)); | |
| 155 exp = -exp; | |
| 156 if (exp > 25) { // underflow | |
| 157 #ifdef SK_CPU_FLUSH_TO_ZERO | |
| 158 // The iOS ARM processor discards small denormalized numbers to go faste
r. | |
| 159 // The comparision below empirically causes the result to agree with the | |
| 160 // tests in MathTest test_float_ceil | |
| 161 if (exp > 149) { | |
| 162 return 0; | |
| 163 } | |
| 164 return 0 < value; | |
| 165 #else | |
| 166 exp = 25; | |
| 167 #endif | |
| 168 } | |
| 169 int add = (1 << exp) - 1; | |
| 170 return (value + add) >> exp; | |
| 171 } | |
| 172 } | |
| 173 | |
| 174 float SkIntToFloatCast(int32_t value) { | |
| 175 if (0 == value) { | |
| 176 return 0; | |
| 177 } | |
| 178 | |
| 179 int shift = EXP_BIAS; | |
| 180 | |
| 181 // record the sign and make value positive | |
| 182 int sign = SkExtractSign(value); | |
| 183 value = SkApplySign(value, sign); | |
| 184 | |
| 185 if (value >> 24) { // value is too big (has more than 24 bits set) | |
| 186 int bias = 8 - SkCLZ(value); | |
| 187 SkDebugf("value = %d, bias = %d\n", value, bias); | |
| 188 SkASSERT(bias > 0 && bias < 8); | |
| 189 value >>= bias; // need to round? | |
| 190 shift += bias; | |
| 191 } else { | |
| 192 int zeros = SkCLZ(value << 8); | |
| 193 SkASSERT(zeros >= 0 && zeros <= 23); | |
| 194 value <<= zeros; | |
| 195 shift -= zeros; | |
| 196 } | |
| 197 | |
| 198 // now value is left-aligned to 24 bits | |
| 199 SkASSERT((value >> 23) == 1); | |
| 200 SkASSERT(shift >= 0 && shift <= 255); | |
| 201 | |
| 202 SkFloatIntUnion data; | |
| 203 data.fSignBitInt = SkLeftShift(sign, 31) | SkLeftShift(shift, 23) | (value &
~MATISSA_MAGIC_BIG); | |
| 204 return data.fFloat; | |
| 205 } | |
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Chromium Code Reviews
Issue 2012333003:
Clean up SkFloatBits (Closed)
Base URL: https://skia.googlesource.com/skia.git@master