1 files changed, 8 insertions, 55 deletions
diff --git a/libgo/go/math/big/nat.go b/libgo/go/math/big/nat.go
index 9b1a626c4cf..889eacb90f0 100644
--- a/libgo/go/math/big/nat.go
+++ b/libgo/go/math/big/nat.go
@@ -9,6 +9,7 @@
 package big
 
 import (
+	"math/bits"
 	"math/rand"
 	"sync"
 )
@@ -67,24 +68,14 @@ func (z nat) setWord(x Word) nat {
 }
 
 func (z nat) setUint64(x uint64) nat {
-	// single-digit values
+	// single-word value
 	if w := Word(x); uint64(w) == x {
 		return z.setWord(w)
 	}
-
-	// compute number of words n required to represent x
-	n := 0
-	for t := x; t > 0; t >>= _W {
-		n++
-	}
-
-	// split x into n words
-	z = z.make(n)
-	for i := range z {
-		z[i] = Word(x & _M)
-		x >>= _W
-	}
-
+	// 2-word value
+	z = z.make(2)
+	z[1] = Word(x >> 32)
+	z[0] = Word(x)
 	return z
 }
 
@@ -653,49 +644,11 @@ func (z nat) divLarge(u, uIn, v nat) (q, r nat) {
 // Length of x in bits. x must be normalized.
 func (x nat) bitLen() int {
 	if i := len(x) - 1; i >= 0 {
-		return i*_W + bitLen(x[i])
+		return i*_W + bits.Len(uint(x[i]))
 	}
 	return 0
 }
 
-const deBruijn32 = 0x077CB531
-
-var deBruijn32Lookup = [...]byte{
-	0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
-	31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9,
-}
-
-const deBruijn64 = 0x03f79d71b4ca8b09
-
-var deBruijn64Lookup = [...]byte{
-	0, 1, 56, 2, 57, 49, 28, 3, 61, 58, 42, 50, 38, 29, 17, 4,
-	62, 47, 59, 36, 45, 43, 51, 22, 53, 39, 33, 30, 24, 18, 12, 5,
-	63, 55, 48, 27, 60, 41, 37, 16, 46, 35, 44, 21, 52, 32, 23, 11,
-	54, 26, 40, 15, 34, 20, 31, 10, 25, 14, 19, 9, 13, 8, 7, 6,
-}
-
-// trailingZeroBits returns the number of consecutive least significant zero
-// bits of x.
-func trailingZeroBits(x Word) uint {
-	// x & -x leaves only the right-most bit set in the word. Let k be the
-	// index of that bit. Since only a single bit is set, the value is two
-	// to the power of k. Multiplying by a power of two is equivalent to
-	// left shifting, in this case by k bits. The de Bruijn constant is
-	// such that all six bit, consecutive substrings are distinct.
-	// Therefore, if we have a left shifted version of this constant we can
-	// find by how many bits it was shifted by looking at which six bit
-	// substring ended up at the top of the word.
-	// (Knuth, volume 4, section 7.3.1)
-	switch _W {
-	case 32:
-		return uint(deBruijn32Lookup[((x&-x)*deBruijn32)>>27])
-	case 64:
-		return uint(deBruijn64Lookup[((x&-x)*(deBruijn64&_M))>>58])
-	default:
-		panic("unknown word size")
-	}
-}
-
 // trailingZeroBits returns the number of consecutive least significant zero
 // bits of x.
 func (x nat) trailingZeroBits() uint {
@@ -707,7 +660,7 @@ func (x nat) trailingZeroBits() uint {
 		i++
 	}
 	// x[i] != 0
-	return i*_W + trailingZeroBits(x[i])
+	return i*_W + uint(bits.TrailingZeros(uint(x[i])))
 }
 
 // z = x << s