diff --git a/src/crypto/sha1/sha1block.go b/src/crypto/sha1/sha1block.go
index 1d37544940..321d34351c 100644
--- a/src/crypto/sha1/sha1block.go
+++ b/src/crypto/sha1/sha1block.go
@@ -4,6 +4,10 @@
 
 package sha1
 
+import (
+	"math/bits"
+)
+
 const (
 	_K0 = 0x5A827999
 	_K1 = 0x6ED9EBA1
@@ -33,48 +37,37 @@ func blockGeneric(dig *digest, p []byte) {
 		i := 0
 		for ; i < 16; i++ {
 			f := b&c | (^b)&d
-			a5 := a<<5 | a>>(32-5)
-			b30 := b<<30 | b>>(32-30)
-			t := a5 + f + e + w[i&0xf] + _K0
-			a, b, c, d, e = t, a, b30, c, d
+			t := bits.RotateLeft32(a, 5) + f + e + w[i&0xf] + _K0
+			a, b, c, d, e = t, a, bits.RotateLeft32(b, 30), c, d
 		}
 		for ; i < 20; i++ {
 			tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
 			w[i&0xf] = tmp<<1 | tmp>>(32-1)
 
 			f := b&c | (^b)&d
-			a5 := a<<5 | a>>(32-5)
-			b30 := b<<30 | b>>(32-30)
-			t := a5 + f + e + w[i&0xf] + _K0
-			a, b, c, d, e = t, a, b30, c, d
+			t := bits.RotateLeft32(a, 5) + f + e + w[i&0xf] + _K0
+			a, b, c, d, e = t, a, bits.RotateLeft32(b, 30), c, d
 		}
 		for ; i < 40; i++ {
 			tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
 			w[i&0xf] = tmp<<1 | tmp>>(32-1)
 			f := b ^ c ^ d
-			a5 := a<<5 | a>>(32-5)
-			b30 := b<<30 | b>>(32-30)
-			t := a5 + f + e + w[i&0xf] + _K1
-			a, b, c, d, e = t, a, b30, c, d
+			t := bits.RotateLeft32(a, 5) + f + e + w[i&0xf] + _K1
+			a, b, c, d, e = t, a, bits.RotateLeft32(b, 30), c, d
 		}
 		for ; i < 60; i++ {
 			tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
 			w[i&0xf] = tmp<<1 | tmp>>(32-1)
 			f := ((b | c) & d) | (b & c)
-
-			a5 := a<<5 | a>>(32-5)
-			b30 := b<<30 | b>>(32-30)
-			t := a5 + f + e + w[i&0xf] + _K2
-			a, b, c, d, e = t, a, b30, c, d
+			t := bits.RotateLeft32(a, 5) + f + e + w[i&0xf] + _K2
+			a, b, c, d, e = t, a, bits.RotateLeft32(b, 30), c, d
 		}
 		for ; i < 80; i++ {
 			tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
 			w[i&0xf] = tmp<<1 | tmp>>(32-1)
 			f := b ^ c ^ d
-			a5 := a<<5 | a>>(32-5)
-			b30 := b<<30 | b>>(32-30)
-			t := a5 + f + e + w[i&0xf] + _K3
-			a, b, c, d, e = t, a, b30, c, d
+			t := bits.RotateLeft32(a, 5) + f + e + w[i&0xf] + _K3
+			a, b, c, d, e = t, a, bits.RotateLeft32(b, 30), c, d
 		}
 
 		h0 += a