slightly simpler math.Pow per gri's suggestion

R=gri
DELTA=28  (2 added, 9 deleted, 17 changed)
OCL=19707
CL=19707

diff --git a/src/lib/math/pow.go b/src/lib/math/pow.go
index bdecf1329ec9cdcb8c10ecb197a3aea453422626..22f2aa9968316d52565aa906b832272e0108e00d 100644 (file)
--- a/src/lib/math/pow.go
+++ b/src/lib/math/pow.go
@@ -6,7 +6,7 @@ package math
 
 import "math"
 
-// x^y: exponentation
+// x^y: exponentiation
 export func Pow(x, y float64) float64 {
        // TODO: x or y NaN, ±Inf, maybe ±0.
        switch {
@@ -38,7 +38,9 @@ export func Pow(x, y float64) float64 {
                return Exp(y * Log(x));
        }
 
-       ans := float64(1);
+       // ans = a1 * 2^ae (= 1 for now).
+       a1 := float64(1);
+       ae := 0;
 
        // ans *= x^yf
        if yf != 0 {
@@ -46,42 +48,33 @@ export func Pow(x, y float64) float64 {
                        yf--;
                        yi++;
                }
-               ans = Exp(yf * Log(x));
+               a1 = Exp(yf * Log(x));
        }
 
        // ans *= x^yi
        // by multiplying in successive squarings
        // of x according to bits of yi.
        // accumulate powers of two into exp.
-       // will still have to do ans *= 2^exp later.
        x1, xe := sys.frexp(x);
-       exp := 0;
-       if i := int64(yi); i != 0 {
-               for {
-                       if i&1 == 1 {
-                               ans *= x1;
-                               exp += xe;
-                       }
-                       i >>= 1;
-                       if i == 0 {
-                               break;
-                       }
-                       x1 *= x1;
-                       xe <<= 1;
-                       if x1 < .5 {
-                               x1 += x1;
-                               xe--;
-                       }
+       for i := int64(yi); i != 0; i >>= 1 {
+               if i&1 == 1 {
+                       a1 *= x1;
+                       ae += xe;
+               }
+               x1 *= x1;
+               xe <<= 1;
+               if x1 < .5 {
+                       x1 += x1;
+                       xe--;
                }
        }
 
-       // ans *= 2^exp
+       // ans = a1*2^ae
        // if flip { ans = 1 / ans }
        // but in the opposite order
        if flip {
-               ans = 1 / ans;
-               exp = -exp;
+               a1 = 1 / a1;
+               ae = -ae;
        }
-       return sys.ldexp(ans, exp);
+       return sys.ldexp(a1, ae);
 }
-