Re: [PATCH] Faster **

From: 	"Piotr Fusik" <pfusik@op.pl>
Message-Id:  <00b201c578af$7ad02b40$17d24dd5@piec>

p4raw-id: //depot/perl@25177

diff --git a/pp.c b/pp.c
index cb48bb8..be055a0 100644 (file)
--- a/pp.c
+++ b/pp.c
@@ -900,36 +900,37 @@ PP(pp_pow)
        we're sure it is safe; otherwise we call pow() and try to convert to
        integer afterwards. */
     {
-        SvIV_please(TOPm1s);
-        if (SvIOK(TOPm1s)) {
-            bool baseuok = SvUOK(TOPm1s);
-            UV baseuv;
+       SvIV_please(TOPs);
+       if (SvIOK(TOPs)) {
+           SvIV_please(TOPm1s);
+           if (SvIOK(TOPm1s)) {
+               UV power;
+               bool baseuok;
+               UV baseuv;
 
-            if (baseuok) {
-                baseuv = SvUVX(TOPm1s);
-            } else {
-               const 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 {
+                   const IV iv = SvIVX(TOPs);
+                   if (iv >= 0) {
+                       power = iv;
+                   } else {
+                       goto float_it; /* Can't do negative powers this way.  */
+                   }
+               }
 
-                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.  */
-                    }
-                }
+               baseuok = SvUOK(TOPm1s);
+               if (baseuok) {
+                   baseuv = SvUVX(TOPm1s);
+               } else {
+                   const 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 */
+                   }
+               }
                 /* now we have integer ** positive integer. */
                 is_int = 1;
 
@@ -945,34 +946,28 @@ PP(pp_pow)
                        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.  */
-                       const 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;
-                        }
-                    }
+
+                   if (power & 1) {
+                       result *= base;
+                   }
+                   while (power >>= 1) {
+                       base *= base;
+                       if (power & 1) {
+                           result *= base;
+                       }
+                   }
                     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;
+                   register unsigned int diff = 8 * sizeof(UV);
+                   while (diff >>= 1) {
+                       highbit -= diff;
+                       if (baseuv >> highbit) {
+                           highbit += diff;
+                       }
                    }
                    /* we now have baseuv < 2 ** highbit */
                    if (power * highbit <= 8 * sizeof(UV)) {
@@ -980,13 +975,14 @@ PP(pp_pow)
                           on same algorithm as above */
                        register UV result = 1;
                        register UV base = baseuv;
-                       register int n = 0;
-                       for (; power; base *= base, n++) {
-                           register const UV bit = (UV)1 << (UV)n;
-                           if (power & bit) {
+                       const bool odd_power = (bool)(power & 1);
+                       if (odd_power) {
+                           result *= base;
+                       }
+                       while (power >>= 1) {
+                           base *= base;
+                           if (power & 1) {
                                result *= base;
-                               power -= bit;
-                               if (power == 0) break;
                            }
                        }
                        SP--;