big: removed some gratuitous +/-1's

R=mtj, bradfitz
CC=golang-dev
https://golang.org/cl/4584046

diff --git a/src/pkg/big/nat.go b/src/pkg/big/nat.go
index ea1903b166fc1602be50cd146d4cd117033dfcdc..734568e068cdaabe08312c0fdf43d36fc4516bf7 100755 (executable)
--- a/src/pkg/big/nat.go
+++ b/src/pkg/big/nat.go
@@ -764,13 +764,12 @@ func (x nat) string(charset string) string {
        if b == b&-b {
                // shift is base-b digit size in bits
                shift := uint(trailingZeroBits(b)) // shift > 0 because b >= 2
-               m := len(x)
                mask := Word(1)<<shift - 1
                w := x[0]
                nbits := uint(_W) // number of unprocessed bits in w
 
                // convert less-significant words
-               for k := 0; k < m-1; k++ {
+               for k := 1; k < len(x); k++ {
                        // convert full digits
                        for nbits >= shift {
                                i--
@@ -782,16 +781,16 @@ func (x nat) string(charset string) string {
                        // convert any partial leading digit and advance to next word
                        if nbits == 0 {
                                // no partial digit remaining, just advance
-                               w = x[k+1]
+                               w = x[k]
                                nbits = _W
                        } else {
-                               // partial digit in current (k) and next (k+1) word
-                               w |= x[k+1] << nbits
+                               // partial digit in current (k-1) and next (k) word
+                               w |= x[k] << nbits
                                i--
                                s[i] = charset[w&mask]
 
                                // advance
-                               w = x[k+1] >> (shift - nbits)
+                               w = x[k] >> (shift - nbits)
                                nbits = _W - (shift - nbits)
                        }
                }