100 lines
1.7 KiB
C
100 lines
1.7 KiB
C
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/*
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libc/ieee_float/ldexp.c
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Created: Oct 14, 1993 by Philip Homburg <philip@cs.vu.nl>
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Implementation of ldexp that directly manipulates the exponent bits in an
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ieee float
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*/
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#include <sys/types.h>
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#include <errno.h>
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#include <math.h>
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#include "ieee_float.h"
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double ldexp(value, exp)
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double value;
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int exp;
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{
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struct f64 *f64p;
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int oldexp, exp_bias;
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double factor;
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f64p= (struct f64 *)&value;
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exp_bias= 0;
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oldexp= F64_GET_EXP(f64p);
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if (oldexp == F64_EXP_MAX)
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{ /* Either infinity or Nan */
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return value;
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}
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if (oldexp == 0)
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{
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/* Either 0 or denormal */
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if (F64_GET_MANT_LOW(f64p) == 0 &&
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F64_GET_MANT_HIGH(f64p) == 0)
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{
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return value;
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}
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}
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/* If exp is too large (> 2*F64_EXP_MAX) or too small
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* (< -2*F64_EXP_MAX) return HUGE_VAL or 0. This prevents overflows
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* in exp if exp is really weird
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*/
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if (exp >= 2*F64_EXP_MAX)
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{
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errno= ERANGE;
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return HUGE_VAL;
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}
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if (exp <= -2*F64_EXP_MAX)
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{
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errno= ERANGE;
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return 0;
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}
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/* Normalize a denormal */
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if (oldexp == 0)
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{
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/* Multiply by 2^64 */
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factor= 65536.0; /* 2^16 */
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factor *= factor; /* 2^32 */
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factor *= factor; /* 2^64 */
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value *= factor;
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exp= -64;
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oldexp= F64_GET_EXP(f64p);
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}
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exp= oldexp + exp;
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if (exp >= F64_EXP_MAX)
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{ /* Overflow */
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errno= ERANGE;
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return HUGE_VAL;
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}
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if (exp > 0)
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{
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/* Normal */
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F64_SET_EXP(f64p, exp);
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return value;
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}
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/* Denormal, or underflow. */
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exp += 64;
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F64_SET_EXP(f64p, exp);
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/* Divide by 2^64 */
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factor= 65536.0; /* 2^16 */
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factor *= factor; /* 2^32 */
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factor *= factor; /* 2^64 */
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value /= factor;
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if (value == 0.0)
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{
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/* Underflow */
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errno= ERANGE;
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}
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return value;
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}
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/*
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* $PchId: ldexp.c,v 1.3 1996/02/22 21:01:39 philip Exp $
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*/
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