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Annotation of coherent/d/usr/lib/libmp/pow.c, revision 1.1.1.1

1.1       root        1: #include "mprec.h"
                      2: 
                      3: 
                      4: /*
                      5:  *     Pow sets the mint pointed to by "c" to the mint pointed to by "a"
                      6:  *     raised to the mint pointed to by "b" power reduced modulo the
                      7:  *     mint pointed to by "m".  If "b" is negative then
                      8:  *     mperr is called with the appropriate error message.
                      9:  *     Note that no assumption is made as to the distinctness of "a", "b",
                     10:  *     "m" and "c".
                     11:  */
                     12: 
                     13: void
                     14: pow(a, b, m, c)
                     15: mint *a, *b, *c;
                     16: register mint *m;
                     17: {
                     18:        mint    al, bl, cl, quot;
                     19:        int rem;
                     20: 
                     21:        if (!ispos(b))
                     22:                mperr("negative power");
                     23: 
                     24:        /* make local copies of a (reduced mod m) and b */
                     25:        minit(&al);
                     26:        minit(&quot);
                     27:        mdiv(a, m, &quot, &al);
                     28:        minit(&bl);
                     29:        mcopy(b, &bl);
                     30: 
                     31:        /* form actual power */
                     32:        minit(&cl);
                     33:        sdiv(&bl, 2, &bl, &rem);
                     34:        if (rem != 0)
                     35:                mcopy(&al, &cl);
                     36:        else
                     37:                mcopy(mone, &cl);
                     38:        while (!zerop(&bl)) {
                     39:                mult(&al, &al, &al);
                     40:                mdiv(&al, m, &quot, &al);
                     41:                sdiv(&bl, 2, &bl, &rem);
                     42:                if (rem != 0) {
                     43:                        mult(&cl, &al, &cl);
                     44:                        mdiv(&cl, m, &quot, &cl);
                     45:                }
                     46:        }
                     47: 
                     48:        /* clean up garbage */
                     49:        mpfree(al.val);
                     50:        mpfree(bl.val);
                     51:        mintfr(quot.val);
                     52:        *c = cl;
                     53: }

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