michael@0: /*
michael@0:  * Copyright 2011 Google Inc.
michael@0:  *
michael@0:  * Use of this source code is governed by a BSD-style license that can be
michael@0:  * found in the LICENSE file.
michael@0:  */
michael@0: 
michael@0: #include "SkFloatBits.h"
michael@0: #include "SkMathPriv.h"
michael@0: 
michael@0: /******************************************************************************
michael@0:     SkFloatBits_toInt[Floor, Round, Ceil] are identical except for what they
michael@0:     do right before they return ... >> exp;
michael@0:     Floor - adds nothing
michael@0:     Round - adds 1 << (exp - 1)
michael@0:     Ceil - adds (1 << exp) - 1
michael@0: 
michael@0:     Floor and Cast are very similar, but Cast applies its sign after all other
michael@0:     computations on value. Also, Cast does not need to check for negative zero,
michael@0:     as that value (0x80000000) "does the right thing" for Ceil. Note that it
michael@0:     doesn't for Floor/Round/Ceil, hence the explicit check.
michael@0: ******************************************************************************/
michael@0: 
michael@0: #define EXP_BIAS            (127+23)
michael@0: #define MATISSA_MAGIC_BIG   (1 << 23)
michael@0: 
michael@0: static inline int unpack_exp(uint32_t packed) {
michael@0:     return (packed << 1 >> 24);
michael@0: }
michael@0: 
michael@0: #if 0
michael@0: // the ARM compiler generates an extra BIC, so I use the dirty version instead
michael@0: static inline int unpack_matissa(uint32_t packed) {
michael@0:     // we could mask with 0x7FFFFF, but that is harder for ARM to encode
michael@0:     return (packed & ~0xFF000000) | MATISSA_MAGIC_BIG;
michael@0: }
michael@0: #endif
michael@0: 
michael@0: // returns the low 24-bits, so we need to OR in the magic_bit afterwards
michael@0: static inline int unpack_matissa_dirty(uint32_t packed) {
michael@0:     return packed & ~0xFF000000;
michael@0: }
michael@0: 
michael@0: // same as (int)float
michael@0: int32_t SkFloatBits_toIntCast(int32_t packed) {
michael@0:     int exp = unpack_exp(packed) - EXP_BIAS;
michael@0:     int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG;
michael@0: 
michael@0:     if (exp >= 0) {
michael@0:         if (exp > 7) {    // overflow
michael@0:             value = SK_MaxS32;
michael@0:         } else {
michael@0:             value <<= exp;
michael@0:         }
michael@0:     } else {
michael@0:         exp = -exp;
michael@0:         if (exp > 25) {   // underflow
michael@0:             exp = 25;
michael@0:         }
michael@0:         value >>= exp;
michael@0:     }
michael@0:     return SkApplySign(value, SkExtractSign(packed));
michael@0: }
michael@0: 
michael@0: // same as (int)floor(float)
michael@0: int32_t SkFloatBits_toIntFloor(int32_t packed) {
michael@0:     // curse you negative 0
michael@0:     if ((packed << 1) == 0) {
michael@0:         return 0;
michael@0:     }
michael@0: 
michael@0:     int exp = unpack_exp(packed) - EXP_BIAS;
michael@0:     int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG;
michael@0: 
michael@0:     if (exp >= 0) {
michael@0:         if (exp > 7) {    // overflow
michael@0:             value = SK_MaxS32;
michael@0:         } else {
michael@0:             value <<= exp;
michael@0:         }
michael@0:         // apply the sign after we check for overflow
michael@0:         return SkApplySign(value, SkExtractSign(packed));
michael@0:     } else {
michael@0:         // apply the sign before we right-shift
michael@0:         value = SkApplySign(value, SkExtractSign(packed));
michael@0:         exp = -exp;
michael@0:         if (exp > 25) {   // underflow
michael@0:             exp = 25;
michael@0:         }
michael@0:         // int add = 0;
michael@0:         return value >> exp;
michael@0:     }
michael@0: }
michael@0: 
michael@0: // same as (int)floor(float + 0.5)
michael@0: int32_t SkFloatBits_toIntRound(int32_t packed) {
michael@0:     // curse you negative 0
michael@0:     if ((packed << 1) == 0) {
michael@0:         return 0;
michael@0:     }
michael@0: 
michael@0:     int exp = unpack_exp(packed) - EXP_BIAS;
michael@0:     int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG;
michael@0: 
michael@0:     if (exp >= 0) {
michael@0:         if (exp > 7) {    // overflow
michael@0:             value = SK_MaxS32;
michael@0:         } else {
michael@0:             value <<= exp;
michael@0:         }
michael@0:         // apply the sign after we check for overflow
michael@0:         return SkApplySign(value, SkExtractSign(packed));
michael@0:     } else {
michael@0:         // apply the sign before we right-shift
michael@0:         value = SkApplySign(value, SkExtractSign(packed));
michael@0:         exp = -exp;
michael@0:         if (exp > 25) {   // underflow
michael@0:             exp = 25;
michael@0:         }
michael@0:         int add = 1 << (exp - 1);
michael@0:         return (value + add) >> exp;
michael@0:     }
michael@0: }
michael@0: 
michael@0: // same as (int)ceil(float)
michael@0: int32_t SkFloatBits_toIntCeil(int32_t packed) {
michael@0:     // curse you negative 0
michael@0:     if ((packed << 1) == 0) {
michael@0:         return 0;
michael@0:     }
michael@0: 
michael@0:     int exp = unpack_exp(packed) - EXP_BIAS;
michael@0:     int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG;
michael@0: 
michael@0:     if (exp >= 0) {
michael@0:         if (exp > 7) {    // overflow
michael@0:             value = SK_MaxS32;
michael@0:         } else {
michael@0:             value <<= exp;
michael@0:         }
michael@0:         // apply the sign after we check for overflow
michael@0:         return SkApplySign(value, SkExtractSign(packed));
michael@0:     } else {
michael@0:         // apply the sign before we right-shift
michael@0:         value = SkApplySign(value, SkExtractSign(packed));
michael@0:         exp = -exp;
michael@0:         if (exp > 25) {   // underflow
michael@0:             exp = 25;
michael@0:         }
michael@0:         int add = (1 << exp) - 1;
michael@0:         return (value + add) >> exp;
michael@0:     }
michael@0: }
michael@0: 
michael@0: float SkIntToFloatCast(int32_t value) {
michael@0:     if (0 == value) {
michael@0:         return 0;
michael@0:     }
michael@0: 
michael@0:     int shift = EXP_BIAS;
michael@0: 
michael@0:     // record the sign and make value positive
michael@0:     int sign = SkExtractSign(value);
michael@0:     value = SkApplySign(value, sign);
michael@0: 
michael@0:     if (value >> 24) {    // value is too big (has more than 24 bits set)
michael@0:         int bias = 8 - SkCLZ(value);
michael@0:         SkDebugf("value = %d, bias = %d\n", value, bias);
michael@0:         SkASSERT(bias > 0 && bias < 8);
michael@0:         value >>= bias; // need to round?
michael@0:         shift += bias;
michael@0:     } else {
michael@0:         int zeros = SkCLZ(value << 8);
michael@0:         SkASSERT(zeros >= 0 && zeros <= 23);
michael@0:         value <<= zeros;
michael@0:         shift -= zeros;
michael@0:     }
michael@0: 
michael@0:     // now value is left-aligned to 24 bits
michael@0:     SkASSERT((value >> 23) == 1);
michael@0:     SkASSERT(shift >= 0 && shift <= 255);
michael@0: 
michael@0:     SkFloatIntUnion data;
michael@0:     data.fSignBitInt = (sign << 31) | (shift << 23) | (value & ~MATISSA_MAGIC_BIG);
michael@0:     return data.fFloat;
michael@0: }
michael@0: 
michael@0: float SkIntToFloatCast_NoOverflowCheck(int32_t value) {
michael@0:     if (0 == value) {
michael@0:         return 0;
michael@0:     }
michael@0: 
michael@0:     int shift = EXP_BIAS;
michael@0: 
michael@0:     // record the sign and make value positive
michael@0:     int sign = SkExtractSign(value);
michael@0:     value = SkApplySign(value, sign);
michael@0: 
michael@0:     int zeros = SkCLZ(value << 8);
michael@0:     value <<= zeros;
michael@0:     shift -= zeros;
michael@0: 
michael@0:     SkFloatIntUnion data;
michael@0:     data.fSignBitInt = (sign << 31) | (shift << 23) | (value & ~MATISSA_MAGIC_BIG);
michael@0:     return data.fFloat;
michael@0: }