github.com/afumu/libc@v0.0.6/musl/src/math/ceil.c (about)

     1  #include "libm.h"
     2  
     3  #if FLT_EVAL_METHOD==0 || FLT_EVAL_METHOD==1
     4  #define EPS DBL_EPSILON
     5  #elif FLT_EVAL_METHOD==2
     6  #define EPS LDBL_EPSILON
     7  #endif
     8  static const double_t toint = 1/EPS;
     9  
    10  double ceil(double x)
    11  {
    12  	union {double f; uint64_t i;} u = {x};
    13  	int e = u.i >> 52 & 0x7ff;
    14  	double_t y;
    15  
    16  	if (e >= 0x3ff+52 || x == 0)
    17  		return x;
    18  	/* y = int(x) - x, where int(x) is an integer neighbor of x */
    19  	if (u.i >> 63)
    20  		y = x - toint + toint - x;
    21  	else
    22  		y = x + toint - toint - x;
    23  	/* special case because of non-nearest rounding modes */
    24  	if (e <= 0x3ff-1) {
    25  		FORCE_EVAL(y);
    26  		return u.i >> 63 ? -0.0 : 1;
    27  	}
    28  	if (y < 0)
    29  		return x + y + 1;
    30  	return x + y;
    31  }