| Kai Tietz | 518dd33 | 2007-08-10 09:54:15 +0000 | [diff] [blame^] | 1 | #include <math.h>
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| 2 | #include <errno.h>
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| 3 | #include "fastmath.h"
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| 4 |
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| 5 | /* acosh(x) = log (x + sqrt(x * x - 1)) */
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| 6 | double acosh (double x)
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| 7 | {
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| 8 | if (isnan (x))
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| 9 | return x;
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| 10 |
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| 11 | if (x < 1.0)
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| 12 | {
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| 13 | errno = EDOM;
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| 14 | return nan("");
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| 15 | }
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| 16 |
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| 17 | if (x > 0x1p32)
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| 18 | /* Avoid overflow (and unnecessary calculation when
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| 19 | sqrt (x * x - 1) == x). GCC optimizes by replacing
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| 20 | the long double M_LN2 const with a fldln2 insn. */
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| 21 | return __fast_log (x) + 6.9314718055994530941723E-1L;
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| 22 |
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| 23 | /* Since x >= 1, the arg to log will always be greater than
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| 24 | the fyl2xp1 limit (approx 0.29) so just use logl. */
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| 25 | return __fast_log (x + __fast_sqrt((x + 1.0) * (x - 1.0)));
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| 26 | }
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