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#include <stdint.h>
#include <math.h>
#include "libm.h"
#include "sqrt_data.h"
#define FENV_SUPPORT 1
static inline uint32_t mul32(uint32_t a, uint32_t b)
{
return (uint64_t)a*b >> 32;
}
/* see sqrt.c for more detailed comments. */
float sqrtf(float x)
{
uint32_t ix, m, m1, m0, even, ey;
ix = asuint(x);
if (predict_false(ix - 0x00800000 >= 0x7f800000 - 0x00800000)) {
/* x < 0x1p-126 or inf or nan. */
if (ix * 2 == 0)
return x;
if (ix == 0x7f800000)
return x;
if (ix > 0x7f800000)
return __math_invalidf(x);
/* x is subnormal, normalize it. */
ix = asuint(x * 0x1p23f);
ix -= 23 << 23;
}
/* x = 4^e m; with int e and m in [1, 4). */
even = ix & 0x00800000;
m1 = (ix << 8) | 0x80000000;
m0 = (ix << 7) & 0x7fffffff;
m = even ? m0 : m1;
/* 2^e is the exponent part of the return value. */
ey = ix >> 1;
ey += 0x3f800000 >> 1;
ey &= 0x7f800000;
/* compute r ~ 1/sqrt(m), s ~ sqrt(m) with 2 goldschmidt iterations. */
static const uint32_t three = 0xc0000000;
uint32_t r, s, d, u, i;
i = (ix >> 17) % 128;
r = (uint32_t)__rsqrt_tab[i] << 16;
/* |r*sqrt(m) - 1| < 0x1p-8 */
s = mul32(m, r);
/* |s/sqrt(m) - 1| < 0x1p-8 */
d = mul32(s, r);
u = three - d;
r = mul32(r, u) << 1;
/* |r*sqrt(m) - 1| < 0x1.7bp-16 */
s = mul32(s, u) << 1;
/* |s/sqrt(m) - 1| < 0x1.7bp-16 */
d = mul32(s, r);
u = three - d;
s = mul32(s, u);
/* -0x1.03p-28 < s/sqrt(m) - 1 < 0x1.fp-31 */
s = (s - 1)>>6;
/* s < sqrt(m) < s + 0x1.08p-23 */
/* compute nearest rounded result. */
uint32_t d0, d1, d2;
float y, t;
d0 = (m << 16) - s*s;
d1 = s - d0;
d2 = d1 + s + 1;
s += d1 >> 31;
s &= 0x007fffff;
s |= ey;
y = asfloat(s);
if (FENV_SUPPORT) {
/* handle rounding and inexact exception. */
uint32_t tiny = predict_false(d2==0) ? 0 : 0x01000000;
tiny |= (d1^d2) & 0x80000000;
t = asfloat(tiny);
y = eval_as_float(y + t);
}
return y;
}
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