src/math/ilogb.c

570af302Sopenharmony_ci#include <limits.h>
570af302Sopenharmony_ci#include "libm.h"
570af302Sopenharmony_ci
570af302Sopenharmony_ciint ilogb(double x)
570af302Sopenharmony_ci{
570af302Sopenharmony_ci	#pragma STDC FENV_ACCESS ON
570af302Sopenharmony_ci	union {double f; uint64_t i;} u = {x};
570af302Sopenharmony_ci	uint64_t i = u.i;
570af302Sopenharmony_ci	int e = i>>52 & 0x7ff;
570af302Sopenharmony_ci
570af302Sopenharmony_ci	if (!e) {
570af302Sopenharmony_ci		i <<= 12;
570af302Sopenharmony_ci		if (i == 0) {
570af302Sopenharmony_ci			FORCE_EVAL(0/0.0f);
570af302Sopenharmony_ci			return FP_ILOGB0;
570af302Sopenharmony_ci		}
570af302Sopenharmony_ci		/* subnormal x */
570af302Sopenharmony_ci		for (e = -0x3ff; i>>63 == 0; e--, i<<=1);
570af302Sopenharmony_ci		return e;
570af302Sopenharmony_ci	}
570af302Sopenharmony_ci	if (e == 0x7ff) {
570af302Sopenharmony_ci		FORCE_EVAL(0/0.0f);
570af302Sopenharmony_ci		return i<<12 ? FP_ILOGBNAN : INT_MAX;
570af302Sopenharmony_ci	}
570af302Sopenharmony_ci	return e - 0x3ff;
570af302Sopenharmony_ci}