+ SvIV_please(TOPm1s);
+ if (SvIOK(TOPm1s)) {
+ bool baseuok = SvUOK(TOPm1s);
+ UV baseuv;
+
+ if (baseuok) {
+ baseuv = SvUVX(TOPm1s);
+ } else {
+ IV iv = SvIVX(TOPm1s);
+ if (iv >= 0) {
+ baseuv = iv;
+ baseuok = TRUE; /* effectively it's a UV now */
+ } else {
+ baseuv = -iv; /* abs, baseuok == false records sign */
+ }
+ }
+ SvIV_please(TOPs);
+ if (SvIOK(TOPs)) {
+ UV power;
+
+ if (SvUOK(TOPs)) {
+ power = SvUVX(TOPs);
+ } else {
+ IV iv = SvIVX(TOPs);
+ if (iv >= 0) {
+ power = iv;
+ } else {
+ goto float_it; /* Can't do negative powers this way. */
+ }
+ }
+ /* now we have integer ** positive integer. */
+ is_int = 1;
+
+ /* foo & (foo - 1) is zero only for a power of 2. */
+ if (!(baseuv & (baseuv - 1))) {
+ /* We are raising power-of-2 to a positive integer.
+ The logic here will work for any base (even non-integer
+ bases) but it can be less accurate than
+ pow (base,power) or exp (power * log (base)) when the
+ intermediate values start to spill out of the mantissa.
+ With powers of 2 we know this can't happen.
+ And powers of 2 are the favourite thing for perl
+ programmers to notice ** not doing what they mean. */
+ NV result = 1.0;
+ NV base = baseuok ? baseuv : -(NV)baseuv;
+ int n = 0;
+
+ for (; power; base *= base, n++) {
+ /* Do I look like I trust gcc with long longs here?
+ Do I hell. */
+ UV bit = (UV)1 << (UV)n;
+ if (power & bit) {
+ result *= base;
+ /* Only bother to clear the bit if it is set. */
+ power -= bit;
+ /* Avoid squaring base again if we're done. */
+ if (power == 0) break;
+ }
+ }
+ SP--;
+ SETn( result );
+ SvIV_please(TOPs);
+ RETURN;
+ } else {
+ register unsigned int highbit = 8 * sizeof(UV);
+ register unsigned int lowbit = 0;
+ register unsigned int diff;
+ bool odd_power = (bool)(power & 1);
+ while ((diff = (highbit - lowbit) >> 1)) {
+ if (baseuv & ~((1 << (lowbit + diff)) - 1))
+ lowbit += diff;
+ else
+ highbit -= diff;
+ }
+ /* we now have baseuv < 2 ** highbit */
+ if (power * highbit <= 8 * sizeof(UV)) {
+ /* result will definitely fit in UV, so use UV math
+ on same algorithm as above */
+ register UV result = 1;
+ register UV base = baseuv;
+ register int n = 0;
+ for (; power; base *= base, n++) {
+ register UV bit = (UV)1 << (UV)n;
+ if (power & bit) {
+ result *= base;
+ power -= bit;
+ if (power == 0) break;
+ }
+ }
+ SP--;
+ if (baseuok || !odd_power)
+ /* answer is positive */
+ SETu( result );
+ else if (result <= (UV)IV_MAX)
+ /* answer negative, fits in IV */
+ SETi( -(IV)result );
+ else if (result == (UV)IV_MIN)
+ /* 2's complement assumption: special case IV_MIN */
+ SETi( IV_MIN );
+ else
+ /* answer negative, doesn't fit */
+ SETn( -(NV)result );
+ RETURN;
+ }
+ }
+ }
+ }
+ }
+ float_it:
+#endif
+ {
+ dPOPTOPnnrl;
+ SETn( Perl_pow( left, right) );
+#ifdef PERL_PRESERVE_IVUV
+ if (is_int)
+ SvIV_please(TOPs);
+#endif
+ RETURN;