34 lines
576 B
C
34 lines
576 B
C
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#include <math.h>
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#include <stdint.h>
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double scalbn(double x, int n)
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{
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union {double f; uint64_t i;} u;
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double_t y = x;
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if (n > 1023) {
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y *= 0x1p1023;
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n -= 1023;
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if (n > 1023) {
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y *= 0x1p1023;
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n -= 1023;
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if (n > 1023)
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n = 1023;
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}
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} else if (n < -1022) {
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/* make sure final n < -53 to avoid double
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rounding in the subnormal range */
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y *= 0x1p-1022 * 0x1p53;
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n += 1022 - 53;
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if (n < -1022) {
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y *= 0x1p-1022 * 0x1p53;
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n += 1022 - 53;
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if (n < -1022)
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n = -1022;
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}
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}
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u.i = (uint64_t)(0x3ff+n)<<52;
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x = y * u.f;
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return x;
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}
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