math: optimize ceil/floor functions on amd64

Use SSE 4.1 rounding instruction to perform rounding
Results (haswell):

name      old time/op  new time/op  delta
Floor-48  2.71ns ± 0%  1.87ns ± 1%  -31.17%  (p=0.000 n=16+19)
Ceil-48   3.09ns ± 3%  2.16ns ± 0%  -30.16%  (p=0.000 n=19+12)

Change-Id: If63715879eed6530b1eb4fc96132d827f8f43909
Reviewed-on: https://go-review.googlesource.com/14561
Reviewed-by: Klaus Post <klauspost@gmail.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/internal/obj/x86/a.out.go

@@ -734,6 +734,11 @@ const (
 	AAESIMC
 	AAESKEYGENASSIST
 
+	AROUNDPS
+	AROUNDSS
+	AROUNDPD
+	AROUNDSD
+
 	APSHUFD
 	APCLMULQDQ
 

src/cmd/internal/obj/x86/anames.go

@@ -677,6 +677,10 @@ var Anames = []string{
 	"AESDECLAST",
 	"AESIMC",
 	"AESKEYGENASSIST",
+	"ROUNDPS",
+	"ROUNDSS",
+	"ROUNDPD",
+	"ROUNDSD",
 	"PSHUFD",
 	"PCLMULQDQ",
 	"JCXZW",

src/cmd/internal/obj/x86/asm6.go

@@ -1474,6 +1474,10 @@ var optab =
 	{AAESDECLAST, yaes, Pq, [23]uint8{0x38, 0xdf, 0}},
 	{AAESIMC, yaes, Pq, [23]uint8{0x38, 0xdb, 0}},
 	{AAESKEYGENASSIST, yaes2, Pq, [23]uint8{0x3a, 0xdf, 0}},
+	{AROUNDPD, yaes2, Pq, [23]uint8{0x3a, 0x09, 0}},
+	{AROUNDPS, yaes2, Pq, [23]uint8{0x3a, 0x08, 0}},
+	{AROUNDSD, yaes2, Pq, [23]uint8{0x3a, 0x0b, 0}},
+	{AROUNDSS, yaes2, Pq, [23]uint8{0x3a, 0x0a, 0}},
 	{APSHUFD, yxshuf, Pq, [23]uint8{0x70, 0}},
 	{APCLMULQDQ, yxshuf, Pq, [23]uint8{0x3a, 0x44, 0}},
 	{obj.AUSEFIELD, ynop, Px, [23]uint8{0, 0}},

src/math/floor_amd64.s

@@ -6,8 +6,25 @@
 
 #define Big		0x4330000000000000 // 2**52
 
+// func hasSSE4() bool
+// returns whether SSE4.1 is supported
+TEXT ·hasSSE4(SB),NOSPLIT,$0
+	XORQ AX, AX
+	INCL AX
+	CPUID
+	SHRQ $19, CX
+	ANDQ $1, CX
+	MOVB CX, ret+0(FP)
+	RET
+
 // func Floor(x float64) float64
 TEXT ·Floor(SB),NOSPLIT,$0
+	CMPB    math·useSSE4(SB), $1
+	JNE     nosse4
+	ROUNDSD $1, x+0(FP), X0
+	MOVQ X0, ret+8(FP)
+	RET
+nosse4:
 	MOVQ	x+0(FP), AX
 	MOVQ	$~(1<<63), DX // sign bit mask
 	ANDQ	AX,DX // DX = |x|
@@ -30,6 +47,12 @@ isBig_floor:
 
 // func Ceil(x float64) float64
 TEXT ·Ceil(SB),NOSPLIT,$0
+	CMPB    math·useSSE4(SB), $1
+	JNE     nosse4
+	ROUNDSD $2, x+0(FP), X0
+	MOVQ X0, ret+8(FP)
+	RET
+nosse4:
 	MOVQ	x+0(FP), AX
 	MOVQ	$~(1<<63), DX // sign bit mask
 	MOVQ	AX, BX // BX = copy of x

src/math/floor_asm.go

@@ -0,0 +1,12 @@
+// Copyright 2015 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 amd64 amd64p32
+
+package math
+
+//defined in floor_amd64.s
+func hasSSE4() bool
+
+var useSSE4 = hasSSE4()