source:
asp3_tinet_ecnl_rx/trunk/musl-1.1.18/src/math/scalbn.c
Last change on this file was 337, checked in by , 6 years ago | |
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File size: 576 bytes |
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1 | #include <math.h> |
2 | #include <stdint.h> |
3 | |
4 | double scalbn(double x, int n) |
5 | { |
6 | union {double f; uint64_t i;} u; |
7 | double_t y = x; |
8 | |
9 | if (n > 1023) { |
10 | y *= 0x1p1023; |
11 | n -= 1023; |
12 | if (n > 1023) { |
13 | y *= 0x1p1023; |
14 | n -= 1023; |
15 | if (n > 1023) |
16 | n = 1023; |
17 | } |
18 | } else if (n < -1022) { |
19 | /* make sure final n < -53 to avoid double |
20 | rounding in the subnormal range */ |
21 | y *= 0x1p-1022 * 0x1p53; |
22 | n += 1022 - 53; |
23 | if (n < -1022) { |
24 | y *= 0x1p-1022 * 0x1p53; |
25 | n += 1022 - 53; |
26 | if (n < -1022) |
27 | n = -1022; |
28 | } |
29 | } |
30 | u.i = (uint64_t)(0x3ff+n)<<52; |
31 | x = y * u.f; |
32 | return x; |
33 | } |
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