SFloatBits.h

 
/*
 * Copyright 2008 The Android Open Source Project
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
#ifndef _SFloatBits_DEFINED_
#define _SFloatBits_DEFINED_
 
#include <stdint.h>
 
SNSBEGIN
/** Convert a sign-bit int (i.e. float interpreted as int) into a 2s compliement
    int. This also converts -0 (0x80000000) to 0. Doing this to a float allows
    it to be compared using normal C operators (<, <=, etc.)
*/
static inline int32_t SkSignBitTo2sCompliment(int32_t x)
{
    if (x < 0)
    {
        x &= 0x7FFFFFFF;
        x = -x;
    }
    return x;
}
 
/** Convert a 2s compliment int to a sign-bit (i.e. int interpreted as float).
    This undoes the result of SkSignBitTo2sCompliment().
 */
static inline int32_t Sk2sComplimentToSignBit(int32_t x)
{
    int sign = x >> 31;
    // make x positive
    x = (x ^ sign) - sign;
    // set the sign bit as needed
    x |= sign << 31;
    return x;
}
 
union SkFloatIntUnion {
    float fFloat;
    int32_t fSignBitInt;
};
 
// Helper to see a float as its bit pattern (w/o aliasing warnings)
static inline int32_t SkFloat2Bits(float x)
{
    SkFloatIntUnion data;
    data.fFloat = x;
    return data.fSignBitInt;
}
 
// Helper to see a bit pattern as a float (w/o aliasing warnings)
static inline float SkBits2Float(int32_t floatAsBits)
{
    SkFloatIntUnion data;
    data.fSignBitInt = floatAsBits;
    return data.fFloat;
}
 
/** Return the float as a 2s compliment int. Just to be used to compare floats
    to each other or against positive float-bit-constants (like 0). This does
    not return the int equivalent of the float, just something cheaper for
    compares-only.
 */
static inline int32_t SkFloatAs2sCompliment(float x)
{
    return SkSignBitTo2sCompliment(SkFloat2Bits(x));
}
 
//  Scalar wrappers for float-bit routines
 
#define SFloatAs2sCompliment(x)   SkFloatAs2sCompliment(x)
#define Sk2sComplimentAsScalar(x) Sk2sComplimentAsFloat(x)
 
SNSEND
#endif