1#include "libm.h"
 2
 3/* k is such that k*ln2 has minimal relative error and x - kln2 > log(FLT_MIN) */
 4static const int k = 235;
 5static const float kln2 = 0x1.45c778p+7f;
 6
 7/* expf(x)/2 for x >= log(FLT_MAX), slightly better than 0.5f*expf(x/2)*expf(x/2) */
 8#ifdef __wasilibc_unmodified_upstream // Wasm doesn't have alternate rounding modes
 9float __expo2f(float x, float sign)
10#else
11float __expo2f(float x)
12#endif
13{
14	float scale;
15
16	/* note that k is odd and scale*scale overflows */
17	SET_FLOAT_WORD(scale, (uint32_t)(0x7f + k/2) << 23);
18	/* exp(x - k ln2) * 2**(k-1) */
19#ifdef __wasilibc_unmodified_upstream // Wasm doesn't have alternate rounding modes
20	/* in directed rounding correct sign before rounding or overflow is important */
21	return expf(x - kln2) * (sign * scale) * scale;
22#else
23	return expf(x - kln2) * scale * scale;
24#endif
25}