Function fxBigInt_exp

xs/sources/xsBigInt.c:1619–1669

}

txBigInt *fxBigInt_exp(txMachine* the, txBigInt *r, txBigInt *a, txBigInt *b)
{
#ifndef mxCompile
	if (b->sign)
		mxRangeError("negative exponent");
#endif
	if (fxBigInt_iszero(b)) {
		if (r == NULL)
			r = fxBigInt_alloc(the, 1);
		else {
			r->size = 1;
			r->sign = 0;
		}
		r->data[0] = 1;
	}
	else {
		int i = fxBigInt_bitsize(b) - 1;
		int odd = fxBigInt_isset(b, i);
		txU4 c = fxBigInt_bitsize(a);
		txBigInt *t = fxBigInt_umul1(the, NULL, b, c);
		t = fxBigInt_ulsr1(the, t, t, 5);
#ifndef mxCompile
		if ((t->size > 1) || (t->data[0] > 0xFFFF))
			mxRangeError("too big exponent");
#endif
		c = 2 + t->data[0];
		fxBigInt_free(the, t);
        if (r == NULL)
			r = fxBigInt_alloc(the, c);
   		t = fxBigInt_alloc(the, c);
      	fxBigInt_copy(r, a);
		while (i > 0) {
            i--;
			t = fxBigInt_sqr(the, t, r);
			if ((odd = fxBigInt_isset(b, i))) {
				r->size = c;
				r = fxBigInt_umul(the, r, t, a);
			}
			else {
				txBigInt u = *r;
				*r = *t;
				*t = u;
			}
			t->size = c;
		}
		r->sign = a->sign & odd;
		fxBigInt_free(the, t);
	}
	mxBigInt_meter(r->size);
	return(r);
}

txBigInt *fxBigInt_sqr(txMachine* the, txBigInt *r, txBigInt *a)
{