1 files changed, 91 insertions, 0 deletions
diff --git a/src/runtime/internal/sys/intrinsics.go b/src/runtime/internal/sys/intrinsics.go
new file mode 100644
index 0000000..3c88982
--- /dev/null
+++ b/src/runtime/internal/sys/intrinsics.go
@@ -0,0 +1,91 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !386
+
+// TODO finish intrinsifying 386, deadcode the assembly, remove build tags, merge w/ intrinsics_common
+// TODO replace all uses of CtzXX with TrailingZerosXX; they are the same.
+
+package sys
+
+// Using techniques from http://supertech.csail.mit.edu/papers/debruijn.pdf
+
+const deBruijn64ctz = 0x0218a392cd3d5dbf
+
+var deBruijnIdx64ctz = [64]byte{
+	0, 1, 2, 7, 3, 13, 8, 19,
+	4, 25, 14, 28, 9, 34, 20, 40,
+	5, 17, 26, 38, 15, 46, 29, 48,
+	10, 31, 35, 54, 21, 50, 41, 57,
+	63, 6, 12, 18, 24, 27, 33, 39,
+	16, 37, 45, 47, 30, 53, 49, 56,
+	62, 11, 23, 32, 36, 44, 52, 55,
+	61, 22, 43, 51, 60, 42, 59, 58,
+}
+
+const deBruijn32ctz = 0x04653adf
+
+var deBruijnIdx32ctz = [32]byte{
+	0, 1, 2, 6, 3, 11, 7, 16,
+	4, 14, 12, 21, 8, 23, 17, 26,
+	31, 5, 10, 15, 13, 20, 22, 25,
+	30, 9, 19, 24, 29, 18, 28, 27,
+}
+
+// Ctz64 counts trailing (low-order) zeroes,
+// and if all are zero, then 64.
+func Ctz64(x uint64) int {
+	x &= -x                       // isolate low-order bit
+	y := x * deBruijn64ctz >> 58  // extract part of deBruijn sequence
+	i := int(deBruijnIdx64ctz[y]) // convert to bit index
+	z := int((x - 1) >> 57 & 64)  // adjustment if zero
+	return i + z
+}
+
+// Ctz32 counts trailing (low-order) zeroes,
+// and if all are zero, then 32.
+func Ctz32(x uint32) int {
+	x &= -x                       // isolate low-order bit
+	y := x * deBruijn32ctz >> 27  // extract part of deBruijn sequence
+	i := int(deBruijnIdx32ctz[y]) // convert to bit index
+	z := int((x - 1) >> 26 & 32)  // adjustment if zero
+	return i + z
+}
+
+// Ctz8 returns the number of trailing zero bits in x; the result is 8 for x == 0.
+func Ctz8(x uint8) int {
+	return int(ntz8tab[x])
+}
+
+// Bswap64 returns its input with byte order reversed
+// 0x0102030405060708 -> 0x0807060504030201
+func Bswap64(x uint64) uint64 {
+	c8 := uint64(0x00ff00ff00ff00ff)
+	a := x >> 8 & c8
+	b := (x & c8) << 8
+	x = a | b
+	c16 := uint64(0x0000ffff0000ffff)
+	a = x >> 16 & c16
+	b = (x & c16) << 16
+	x = a | b
+	c32 := uint64(0x00000000ffffffff)
+	a = x >> 32 & c32
+	b = (x & c32) << 32
+	x = a | b
+	return x
+}
+
+// Bswap32 returns its input with byte order reversed
+// 0x01020304 -> 0x04030201
+func Bswap32(x uint32) uint32 {
+	c8 := uint32(0x00ff00ff)
+	a := x >> 8 & c8
+	b := (x & c8) << 8
+	x = a | b
+	c16 := uint32(0x0000ffff)
+	a = x >> 16 & c16
+	b = (x & c16) << 16
+	x = a | b
+	return x
+}