Avoid some cgoCheckPointer calls

zstd.go

@@ -7,13 +7,30 @@ package zstd
 #cgo CFLAGS: -DZSTD_LEGACY_SUPPORT=4 -DZSTD_MULTITHREAD=1
 
 #include "zstd.h"
+
+// These wrappers converting void* arguments to char* are required to convince
+// Go that there are no pointers hiding in there, and that slow runtime checks
+// are unnecessary.
+
+size_t ZSwrapper_compress(unsigned char* dst, size_t dstCapacity, const unsigned char* src, size_t srcSize, int compressionLevel)
+{
+	return ZSTD_compress(dst, dstCapacity, src, srcSize, compressionLevel);
+}
+
+size_t ZSwrapper_decompress(unsigned char* dst, size_t dstCapacity, const unsigned char* src, size_t srcSize)
+{
+	return ZSTD_decompress(dst, dstCapacity, src, srcSize);
+}
+
+unsigned long long ZSwrapper_getFrameContentSize(const unsigned char *src, size_t srcSize) {
+	return ZSTD_getFrameContentSize(src, srcSize);
+}
 */
 import "C"
 import (
 	"bytes"
 	"errors"
 	"io/ioutil"
-	"unsafe"
 )
 
 // Defines best and standard values for zstd cli
@@ -68,7 +85,7 @@ func decompressSizeHint(src []byte) int {
 
 	hint := upperBound
 	if len(src) >= zstdFrameHeaderSizeMin {
-		hint = int(C.ZSTD_getFrameContentSize(unsafe.Pointer(&src[0]), C.size_t(len(src))))
+		hint = int(C.ZSwrapper_getFrameContentSize((*C.uchar)(&src[0]), C.size_t(len(src))))
 		if hint < 0 { // On error, just use upperBound
 			hint = upperBound
 		}
@@ -100,22 +117,19 @@ func CompressLevel(dst, src []byte, level int) ([]byte, error) {
 		dst = make([]byte, bound)
 	}
 
-	// We need unsafe.Pointer(&src[0]) in the Cgo call to avoid "Go pointer to Go pointer" panics.
-	// This means we need to special case empty input. See:
-	// https://github.com/golang/go/issues/14210#issuecomment-346402945
 	var cWritten C.size_t
 	if len(src) == 0 {
-		cWritten = C.ZSTD_compress(
-			unsafe.Pointer(&dst[0]),
+		cWritten = C.ZSwrapper_compress(
+			(*C.uchar)(&dst[0]),
 			C.size_t(len(dst)),
-			unsafe.Pointer(nil),
+			(*C.uchar)(nil),
 			C.size_t(0),
 			C.int(level))
 	} else {
-		cWritten = C.ZSTD_compress(
-			unsafe.Pointer(&dst[0]),
+		cWritten = C.ZSwrapper_compress(
+			(*C.uchar)(&dst[0]),
 			C.size_t(len(dst)),
-			unsafe.Pointer(&src[0]),
+			(*C.uchar)(&src[0]),
 			C.size_t(len(src)),
 			C.int(level))
 	}
@@ -143,10 +157,10 @@ func Decompress(dst, src []byte) ([]byte, error) {
 		dst = make([]byte, bound)
 	}
 
-	written := int(C.ZSTD_decompress(
-		unsafe.Pointer(&dst[0]),
+	written := int(C.ZSwrapper_decompress(
+		(*C.uchar)(&dst[0]),
 		C.size_t(len(dst)),
-		unsafe.Pointer(&src[0]),
+		(*C.uchar)(&src[0]),
 		C.size_t(len(src))))
 	err := getError(written)
 	if err == nil {

zstd_test.go

@@ -336,7 +336,9 @@ func BenchmarkDecompression(b *testing.B) {
 	if err != nil {
 		b.Fatalf("Failed compressing: %s", err)
 	}
-	b.Logf("Reduced from %v to %v", len(raw), len(dst))
+	if b.N == 1 {
+		b.Logf("Reduced from %v to %v", len(raw), len(dst))
+	}
 	b.SetBytes(int64(len(raw)))
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {