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Annotation of coherent/d/lib/libc/crt/_pow10.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * C general utilities library internals.
        !             3:  * _pow10()
        !             4:  * Compute 10.0^n.
        !             5:  * Assumes -319 <= DBL_MIN_10_EXP and DBL_MAX_10_EXP <= 319,
        !             6:  * which is true for IEEE-format doubles.
        !             7:  * Modified for MS-DOS from the standard ANSI library source.
        !             8:  */
        !             9: 
        !            10: /*
        !            11:  * There are lots of ways to do this, with varying accuracy, size, and speed.
        !            12:  * This version is nonrecursive and fast but uses somewhat bulky tables.
        !            13:  * It does the common cases -16 < exp < 16 by table lookup with no fp arithmetic.
        !            14:  * It does 16 <= exp <= DBL_MAX_10_EXP with one fp multiply.
        !            15:  * It does DBL_MIN_10_EXP <= exp <= -16 with one fp divide.
        !            16:  */
        !            17: 
        !            18: #include <math.h>
        !            19: 
        !            20: #if    IEEE
        !            21: #define        DBL_MAX_10_EXP  308
        !            22: #define DBL_MIN_10_EXP -307
        !            23: #else
        !            24: #define        DBL_MAX_10_EXP  38
        !            25: #define DBL_MIN_10_EXP -38
        !            26: #endif
        !            27: 
        !            28: static const double powtab0[] = {
        !            29:        1e0,    1e-1,   1e-2,   1e-3,   1e-4,   1e-5,   1e-6,   1e-7,
        !            30:        1e-8,   1e-9,   1e-10,  1e-11,  1e-12,  1e-13,  1e-14,  1e-15
        !            31: };
        !            32: 
        !            33: static const double powtab1[] = {
        !            34:        1e0,    1e1,    1e2,    1e3,    1e4,    1e5,    1e6,    1e7,
        !            35:        1e8,    1e9,    1e10,   1e11,   1e12,   1e13,   1e14,   1e15
        !            36: };
        !            37: 
        !            38: static const double powtab2[] = {
        !            39: #ifdef IEEE
        !            40:        1e16,   1e32,   1e48,   1e64,   1e80,   1e96,   1e112,  1e128,
        !            41:        1e144,  1e160,  1e176,  1e192,  1e208,  1e224,  1e240,  1e256,
        !            42:        1e272,  1e288,  1e304
        !            43: #else
        !            44:        1e16,   1e32
        !            45: #endif
        !            46: };
        !            47: 
        !            48: double
        !            49: _pow10(exp) register int exp;
        !            50: {
        !            51:        if (exp < 0) {
        !            52:                if ((exp = -exp) < 16)
        !            53:                        return powtab0[exp];
        !            54:                else if (exp <= -DBL_MIN_10_EXP)
        !            55:                        return powtab0[exp & 15] / powtab2[(exp >> 4) - 1];
        !            56:                else
        !            57:                        return 0.0;             /* exponent underflow */
        !            58:        }
        !            59:        else if (exp < 16)
        !            60:                return powtab1[exp];
        !            61:        else if (exp <= DBL_MAX_10_EXP)
        !            62:                return powtab1[exp & 15] * powtab2[(exp >> 4) - 1];
        !            63:        else
        !            64:                return HUGE_VAL;                /* exponent overflow */
        !            65: }

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