37 lines
912 B
C
37 lines
912 B
C
/*
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* ldexp(value, exp) returns the quantity value * 2 ** exp.
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* In the event of overflow, on UNIX a floating-point exception is signalled.
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* In the event of underflow, zero is returned.
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*
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*/
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#include <nan.h>
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#include <values.h>
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/* Largest long int power of 2 */
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#define MAXSHIFT (BITSPERBYTE * sizeof(long) - 2)
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double
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ldexp(value, exp)
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register double value;
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register int exp;
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{
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extern double frexp();
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int old_exp;
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if (exp == 0 || value == 0.0) /* nothing to do for zero */
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return (value);
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frexp(value, &old_exp);
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if (exp > 0) {
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if (exp + old_exp > MAXBEXP) /* overflow */
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KILLFPE();
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for ( ; exp > MAXSHIFT; exp -= MAXSHIFT)
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value *= (1L << MAXSHIFT);
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return (value * (1L << exp));
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}
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if (exp + old_exp < MINBEXP) /* underflow */
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return (0.0);
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for ( ; exp < -MAXSHIFT; exp += MAXSHIFT)
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value *= 1.0/(1L << MAXSHIFT); /* mult faster than div */
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return (value / (1L << -exp));
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}
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