hash/crc32: remove redundant code

Merge the CRC32 Update and Write functions using an unexported function, to avoid duplication of code and make it more readable.
The only difference between them is the check of the initialization of the IEEE table, and a boolean value specifies that.

Throughout the crc32.go file, in the switches the default value is inserted inside the switch statement, this change uniforms the style of the MakeTable function, making it like the other pieces of code.

Change-Id: I3889f6c6671210c82f0d7250cea67907bccf3ce7
GitHub-Last-Rev: b8777ee213f2ebad0bb4a5dcdb812fd356d6d086
GitHub-Pull-Request: golang/go#55044
Reviewed-on: https://go-review.googlesource.com/c/go/+/430456
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Jenny Rakoczy <jenny@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Jenny Rakoczy <jenny@golang.org>
Auto-Submit: Jenny Rakoczy <jenny@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>

diff --git a/src/hash/crc32/crc32.go b/src/hash/crc32/crc32.go
index 4fcb168e6e9b387fa8db552d4d1e7cda66a55c44..e828089308dbad9d12c0575747a8c9aa627b68cb 100644 (file)
--- a/src/hash/crc32/crc32.go
+++ b/src/hash/crc32/crc32.go
@@ -128,8 +128,9 @@ func MakeTable(poly uint32) *Table {
        case Castagnoli:
                castagnoliOnce.Do(castagnoliInit)
                return castagnoliTable
+       default:
+               return simpleMakeTable(poly)
        }
-       return simpleMakeTable(poly)
 }
 
 // digest represents the partial evaluation of a checksum.
@@ -205,32 +206,31 @@ func readUint32(b []byte) uint32 {
        return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
 }
 
-// Update returns the result of adding the bytes in p to the crc.
-func Update(crc uint32, tab *Table, p []byte) uint32 {
+func update(crc uint32, tab *Table, p []byte, checkInitIEEE bool) uint32 {
        switch {
        case haveCastagnoli.Load() && tab == castagnoliTable:
                return updateCastagnoli(crc, p)
        case tab == IEEETable:
-               // Unfortunately, because IEEETable is exported, IEEE may be used without a
-               // call to MakeTable. We have to make sure it gets initialized in that case.
-               ieeeOnce.Do(ieeeInit)
+               if checkInitIEEE {
+                       ieeeOnce.Do(ieeeInit)
+               }
                return updateIEEE(crc, p)
        default:
                return simpleUpdate(crc, tab, p)
        }
 }
 
+// Update returns the result of adding the bytes in p to the crc.
+func Update(crc uint32, tab *Table, p []byte) uint32 {
+       // Unfortunately, because IEEETable is exported, IEEE may be used without a
+       // call to MakeTable. We have to make sure it gets initialized in that case.
+       return update(crc, tab, p, true)
+}
+
 func (d *digest) Write(p []byte) (n int, err error) {
-       switch {
-       case haveCastagnoli.Load() && d.tab == castagnoliTable:
-               d.crc = updateCastagnoli(d.crc, p)
-       case d.tab == IEEETable:
-               // We only create digest objects through New() which takes care of
-               // initialization in this case.
-               d.crc = updateIEEE(d.crc, p)
-       default:
-               d.crc = simpleUpdate(d.crc, d.tab, p)
-       }
+       // We only create digest objects through New() which takes care of
+       // initialization in this case.
+       d.crc = update(d.crc, d.tab, p, false)
        return len(p), nil
 }
 

diff --git a/src/hash/crc32/crc32_test.go b/src/hash/crc32/crc32_test.go
index cbb869dfd641db9a4f912d010da2876092135427..f084612f6f0ff1deeb1768633197960899135b67 100644 (file)
--- a/src/hash/crc32/crc32_test.go
+++ b/src/hash/crc32/crc32_test.go
@@ -329,11 +329,14 @@ func benchmark(b *testing.B, h hash.Hash32, n, alignment int64) {
        h.Reset()
        h.Write(data)
        h.Sum(in)
+       // Avoid further allocations
+       in = in[:0]
 
        b.ResetTimer()
        for i := 0; i < b.N; i++ {
                h.Reset()
                h.Write(data)
                h.Sum(in)
+               in = in[:0]
        }
 }