fmodf.c raw

   1  #include <math.h>
   2  #include <stdint.h>
   3  
   4  float fmodf(float x, float y)
   5  {
   6  	union {float f; uint32_t i;} ux = {x}, uy = {y};
   7  	int ex = ux.i>>23 & 0xff;
   8  	int ey = uy.i>>23 & 0xff;
   9  	uint32_t sx = ux.i & 0x80000000;
  10  	uint32_t i;
  11  	uint32_t uxi = ux.i;
  12  
  13  	if (uy.i<<1 == 0 || isnan(y) || ex == 0xff)
  14  		return (x*y)/(x*y);
  15  	if (uxi<<1 <= uy.i<<1) {
  16  		if (uxi<<1 == uy.i<<1)
  17  			return 0*x;
  18  		return x;
  19  	}
  20  
  21  	/* normalize x and y */
  22  	if (!ex) {
  23  		for (i = uxi<<9; i>>31 == 0; ex--, i <<= 1);
  24  		uxi <<= -ex + 1;
  25  	} else {
  26  		uxi &= -1U >> 9;
  27  		uxi |= 1U << 23;
  28  	}
  29  	if (!ey) {
  30  		for (i = uy.i<<9; i>>31 == 0; ey--, i <<= 1);
  31  		uy.i <<= -ey + 1;
  32  	} else {
  33  		uy.i &= -1U >> 9;
  34  		uy.i |= 1U << 23;
  35  	}
  36  
  37  	/* x mod y */
  38  	for (; ex > ey; ex--) {
  39  		i = uxi - uy.i;
  40  		if (i >> 31 == 0) {
  41  			if (i == 0)
  42  				return 0*x;
  43  			uxi = i;
  44  		}
  45  		uxi <<= 1;
  46  	}
  47  	i = uxi - uy.i;
  48  	if (i >> 31 == 0) {
  49  		if (i == 0)
  50  			return 0*x;
  51  		uxi = i;
  52  	}
  53  	for (; uxi>>23 == 0; uxi <<= 1, ex--);
  54  
  55  	/* scale result up */
  56  	if (ex > 0) {
  57  		uxi -= 1U << 23;
  58  		uxi |= (uint32_t)ex << 23;
  59  	} else {
  60  		uxi >>= -ex + 1;
  61  	}
  62  	uxi |= sx;
  63  	ux.i = uxi;
  64  	return ux.f;
  65  }
  66