source: mainline/uspace/lib/math/generic/scalbn.c@ 21d5236

/*
 * ====================================================
 * Copyright (C) 2004 by Sun Microsystems, Inc. All rights reserved.
 *
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */

/** @addtogroup libmath
 * @{
 */
/** @file scalbn mathematical function
 */

#include <math.h>
#include <stdint.h>


/* scalbn(x,n) returns x* 2**n  computed by  exponent
 * manipulation rather than by actually performing an
 * exponentiation or a multiplication.
 */

double scalbn(double x, int n)
{
        union {double f; uint64_t i;} u;
        double_t y = x;

        if (n > 1023) {
                y *= 0x1p1023;
                n -= 1023;
                if (n > 1023) {
                        y *= 0x1p1023;
                        n -= 1023;
                        if (n > 1023)
                                n = 1023;
                }
        } else if (n < -1022) {
        /* make sure final n < -53 to avoid double
           rounding in the subnormal range */
                y *= 0x1p-1022 * 0x1p53;
                n += 1022 - 53;
                if (n < -1022) {
                        y *= 0x1p-1022 * 0x1p53;
                        n += 1022 - 53;
                        if (n < -1022)
                                n = -1022;
                }
        }
        u.i = (uint64_t)(0x3ff+n)<<52;
        x = y * u.f;

        return x;
}

/** @}
 */