source: soft/giet_vm/giet_libs/math/fmod.c @ 812

/*
 *  fmod.c
 *  cLibm
 *
 *     Written by Jon Okada, started on December 7th, 1992.                      
 *     Modified by Paul Finlayson (PAF) for MathLib v2.                          
 *     Modified by A. Sazegari (ali) for MathLib v3.                             
 *     Modified and ported by Robert A. Murley (ram) for Mac OS X.               
 *     Modified for cLibm, fixed a few edge cases, rewrote local_ funcs by Ian Ollmann.
 *     Modified for armLibm, removed code to set flags as this is a soft-float fallback only.
 *
 *  Copyright 2007 Apple Inc. All rights reserved.
 *
 */

#include "../math.h"
#include "math_private.h"
 
double fmod(double x, double y)
{
    union {
        double d;
        uint64_t u;
    } ux = {x};
    union {
        double d;
        uint64_t u;
    } uy = {y};
    
    uint64_t absx = ux.u & ~0x8000000000000000ULL;
    uint64_t absy = uy.u & ~0x8000000000000000ULL;

    if (absx - 1ULL >= 0x7fefffffffffffffULL || absy - 1ULL >= 0x7fefffffffffffffULL) {
        double fabsx = fabs(x);
        double fabsy = fabs(y);
        
        // deal with NaN
        if (x != x || y != y) {
            return x + y;
        }

        // x = Inf or y = 0, return Invalid per IEEE-754
        if (!isfinite(fabsx) || 0.0 == y) {
            return 0.0 / 0.0; // NaN
        }

        // handle trivial case
        if (!isfinite(fabsy) || 0.0 == x) {
            return x;
        }
    }
 
    if (absy >= absx) {
        if (absy == absx) {
            ux.u ^= absx;
            return ux.d;
        }
        
        return x;
    }
 
    int32_t expx = absx >> 52;
    int32_t expy = absy >> 52;
    int64_t sx = absx & 0x000fffffffffffffULL;
    int64_t sy = absy & 0x000fffffffffffffULL;

    if (0 == expx) {
        uint32_t shift = __builtin_clzll(absx) - (64 - 53);
        sx <<= shift;
        expx = 1 - shift;
    }

    if (0 == expy)
    {
        uint32_t shift = __builtin_clzll(absy) - (64 - 53);
        sy <<= shift;
        expy = 1 - shift;
    }
    sx |= 0x0010000000000000ULL;
    sy |= 0x0010000000000000ULL;


    int32_t idiff = expx - expy;
    int32_t shift = 0;
    int64_t mask;
    
    do {
        sx <<= shift;
        idiff += ~shift;
        sx -= sy;
        mask = sx >> 63;
        sx += sx;
        sx += sy & mask;
        shift = __builtin_clzll(sx) - (64 - 53);
    }
    while (idiff >= shift && sx != 0LL);

    if (idiff < 0) {
        sx += sy & mask;
        sx >>= 1;
        idiff = 0;
    }
    
    sx <<= idiff;
    
    if (0 == sx) {
        ux.u &= 0x8000000000000000ULL;
        return ux.d;
    }
    
    shift = __builtin_clzll(sx) - (64 - 53);
    sx <<= shift;
    expy -= shift;
    sx &= 0x000fffffffffffffULL;
    sx |= ux.u & 0x8000000000000000ULL;
    if (expy > 0) {
        ux.u = sx | ((int64_t) expy << 52);
        return ux.d;
    }
    
    expy += 1022;
    ux.u = sx | ((int64_t) expy << 52);
    return ux.d * 0x1.0p-1022;

}