epoger@google.com | ec3ed6a | 2011-07-28 14:26:00 +0000 | [diff] [blame] | 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 | */ |
reed@google.com | 4b163ed | 2012-08-07 21:35:13 +0000 | [diff] [blame] | 7 | |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 8 | #include "SkFloatBits.h" |
reed@google.com | 4b163ed | 2012-08-07 21:35:13 +0000 | [diff] [blame] | 9 | #include "SkMathPriv.h" |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 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; |
rmistry@google.com | fbfcd56 | 2012-08-23 18:09:54 +0000 | [diff] [blame] | 48 | |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 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 ((packed << 1) == 0) { |
| 69 | return 0; |
| 70 | } |
rmistry@google.com | fbfcd56 | 2012-08-23 18:09:54 +0000 | [diff] [blame] | 71 | |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 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 |
caryclark | 936b734 | 2014-07-11 12:14:51 -0700 | [diff] [blame] | 88 | #ifdef SK_DISCARD_DENORMALIZED_FOR_SPEED |
| 89 | // The iOS ARM processor discards small denormalized numbers to go faster. |
| 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 |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 96 | exp = 25; |
caryclark | 936b734 | 2014-07-11 12:14:51 -0700 | [diff] [blame] | 97 | #endif |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 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 ((packed << 1) == 0) { |
| 108 | return 0; |
| 109 | } |
rmistry@google.com | fbfcd56 | 2012-08-23 18:09:54 +0000 | [diff] [blame] | 110 | |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 111 | int exp = unpack_exp(packed) - EXP_BIAS; |
| 112 | int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG; |
rmistry@google.com | fbfcd56 | 2012-08-23 18:09:54 +0000 | [diff] [blame] | 113 | |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 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 ((packed << 1) == 0) { |
| 138 | return 0; |
| 139 | } |
rmistry@google.com | fbfcd56 | 2012-08-23 18:09:54 +0000 | [diff] [blame] | 140 | |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 141 | int exp = unpack_exp(packed) - EXP_BIAS; |
| 142 | int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG; |
rmistry@google.com | fbfcd56 | 2012-08-23 18:09:54 +0000 | [diff] [blame] | 143 | |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 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 |
caryclark | 936b734 | 2014-07-11 12:14:51 -0700 | [diff] [blame] | 157 | #ifdef SK_DISCARD_DENORMALIZED_FOR_SPEED |
| 158 | // The iOS ARM processor discards small denormalized numbers to go faster. |
| 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 |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 166 | exp = 25; |
caryclark | 936b734 | 2014-07-11 12:14:51 -0700 | [diff] [blame] | 167 | #endif |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 168 | } |
| 169 | int add = (1 << exp) - 1; |
| 170 | return (value + add) >> exp; |
| 171 | } |
| 172 | } |
| 173 | |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 174 | float SkIntToFloatCast(int32_t value) { |
| 175 | if (0 == value) { |
| 176 | return 0; |
| 177 | } |
| 178 | |
| 179 | int shift = EXP_BIAS; |
rmistry@google.com | fbfcd56 | 2012-08-23 18:09:54 +0000 | [diff] [blame] | 180 | |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 181 | // record the sign and make value positive |
| 182 | int sign = SkExtractSign(value); |
| 183 | value = SkApplySign(value, sign); |
rmistry@google.com | fbfcd56 | 2012-08-23 18:09:54 +0000 | [diff] [blame] | 184 | |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 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 | } |
rmistry@google.com | fbfcd56 | 2012-08-23 18:09:54 +0000 | [diff] [blame] | 197 | |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 198 | // now value is left-aligned to 24 bits |
| 199 | SkASSERT((value >> 23) == 1); |
| 200 | SkASSERT(shift >= 0 && shift <= 255); |
rmistry@google.com | fbfcd56 | 2012-08-23 18:09:54 +0000 | [diff] [blame] | 201 | |
reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame] | 202 | SkFloatIntUnion data; |
| 203 | data.fSignBitInt = (sign << 31) | (shift << 23) | (value & ~MATISSA_MAGIC_BIG); |
| 204 | return data.fFloat; |
| 205 | } |