-#include "libm.h"
+#include <math.h>
+#include <stdint.h>
double scalbn(double x, int n)
{
- /* make sure result is stored as double on overflow or underflow */
- volatile double z;
- double scale;
+ union {double f; uint64_t i;} u;
+ double_t y = x;
if (n > 1023) {
- x *= 0x1p1023;
+ y *= 0x1p1023;
n -= 1023;
if (n > 1023) {
- x *= 0x1p1023;
+ y *= 0x1p1023;
n -= 1023;
- if (n > 1023) {
- z = x * 0x1p1023;
- return z;
- }
+ if (n > 1023)
+ n = 1023;
}
} else if (n < -1022) {
- x *= 0x1p-1022;
- n += 1022;
+ /* make sure final n < -53 to avoid double
+ rounding in the subnormal range */
+ y *= 0x1p-1022 * 0x1p53;
+ n += 1022 - 53;
if (n < -1022) {
- x *= 0x1p-1022;
- n += 1022;
- if (n < -1022) {
- z = x * 0x1p-1022;
- return z;
- }
+ y *= 0x1p-1022 * 0x1p53;
+ n += 1022 - 53;
+ if (n < -1022)
+ n = -1022;
}
}
- INSERT_WORDS(scale, (uint32_t)(0x3ff+n)<<20, 0);
- z = x * scale;
- return z;
+ u.i = (uint64_t)(0x3ff+n)<<52;
+ x = y * u.f;
+ return x;
}