strconv: cleanup old compiler bits.TrailingZeros workaround

Since CL 599096 the compiler knows bits.TrailingZeros's maximum value
based on the input type size.

Since CL 603996 it knows it based on input's maximum value.

Change-Id: Ib0d6b15a3ba6894d3e7e12b79b387ddbffabe370
Reviewed-on: https://go-review.googlesource.com/c/go/+/618715
Auto-Submit: Robert Griesemer <gri@google.com>
Commit-Queue: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>

diff --git a/src/strconv/itoa.go b/src/strconv/itoa.go
index 29fec41fe2e4f8463e2b3d36dbd3dfe55ff6a78c..928b37ffa63390c8e813f43e91483fe3e4d75e9b 100644 (file)
--- a/src/strconv/itoa.go
+++ b/src/strconv/itoa.go
@@ -152,13 +152,7 @@ func formatBits(dst []byte, u uint64, base int, neg, append_ bool) (d []byte, s
 
        } else if isPowerOfTwo(base) {
                // Use shifts and masks instead of / and %.
-               // Base is a power of 2 and 2 <= base <= len(digits) where len(digits) is 36.
-               // The largest power of 2 below or equal to 36 is 32, which is 1 << 5;
-               // i.e., the largest possible shift count is 5. By &-ind that value with
-               // the constant 7 we tell the compiler that the shift count is always
-               // less than 8 which is smaller than any register width. This allows
-               // the compiler to generate better code for the shift operation.
-               shift := uint(bits.TrailingZeros(uint(base))) & 7
+               shift := uint(bits.TrailingZeros(uint(base)))
                b := uint64(base)
                m := uint(base) - 1 // == 1<<shift - 1
                for u >= b {