From: Huang Qiqi <huangqiqi@loongson.cn>
Date: Tue, 11 Jun 2024 11:06:29 +0000 (+0800)
Subject: math/big: optimize subVV function for loong64
X-Git-Tag: go1.25rc1~471
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=396a48bea6f2dc07ef103da298eec05cb6167892;p=gostls13.git

math/big: optimize subVV function for loong64

Benchmark results on Loongson 3C5000 (which is an LA464 implementation):

goos: linux
goarch: loong64
pkg: math/big
cpu: Loongson-3C5000 @ 2200.00MHz
             │ test/old_3c5000_subvv.log │      test/new_3c5000_subvv.log      │
             │          sec/op           │   sec/op     vs base                │
SubVV/1                     10.920n ± 0%   7.657n ± 0%  -29.88% (p=0.000 n=20)
SubVV/2                     14.100n ± 0%   8.841n ± 0%  -37.30% (p=0.000 n=20)
SubVV/3                      16.38n ± 0%   11.06n ± 0%  -32.48% (p=0.000 n=20)
SubVV/4                      18.65n ± 0%   12.85n ± 0%  -31.10% (p=0.000 n=20)
SubVV/5                      20.93n ± 0%   14.79n ± 0%  -29.34% (p=0.000 n=20)
SubVV/10                     32.30n ± 0%   22.29n ± 0%  -30.99% (p=0.000 n=20)
SubVV/100                    244.3n ± 0%   149.2n ± 0%  -38.93% (p=0.000 n=20)
SubVV/1000                   2.292µ ± 0%   1.378µ ± 0%  -39.88% (p=0.000 n=20)
SubVV/10000                  26.26µ ± 0%   25.64µ ± 0%   -2.33% (p=0.000 n=20)
SubVV/100000                 341.3µ ± 0%   238.0µ ± 0%  -30.26% (p=0.000 n=20)
geomean                      209.1n        144.5n       -30.86%

Change-Id: I3863c2c6728f1b0f8fecbf77de13254299c5b1cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/659877
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
---

diff --git a/src/math/big/arith_loong64.s b/src/math/big/arith_loong64.s
index 9b22a26553..2a2ffafeef 100644
--- a/src/math/big/arith_loong64.s
+++ b/src/math/big/arith_loong64.s
@@ -12,8 +12,35 @@
 TEXT ·addVV(SB),NOSPLIT,$0
 	JMP ·addVV_g(SB)
 
+// func subVV(z, x, y []Word) (c Word)
 TEXT ·subVV(SB),NOSPLIT,$0
-	JMP ·subVV_g(SB)
+	// input:
+	//   R4: z
+	//   R5: z_len
+	//   R7: x
+	//   R10: y
+	MOVV	z+0(FP), R4
+	MOVV	z_len+8(FP), R5
+	MOVV	x+24(FP), R7
+	MOVV	y+48(FP), R10
+	MOVV	$0, R6
+	SLLV	$3, R5
+	MOVV	$0, R8
+loop:
+	BEQ	R5, R6, done
+	MOVV	(R6)(R7), R9
+	MOVV	(R6)(R10), R11
+	SUBV	R11, R9, R11	// x1 - y1 = z1', if z1' > x1 then overflow
+	SUBV	R8, R11, R12	// z1' - c0 = z1, if z1 > z1' then overflow
+	SGTU	R11, R9, R9
+	SGTU	R12, R11, R11
+	MOVV	R12, (R6)(R4)
+	OR	R9, R11, R8
+	ADDV	$8, R6
+	JMP	loop
+done:
+	MOVV	R8, c+72(FP)
+	RET
 
 // func addVW(z, x []Word, y Word) (c Word)
 TEXT ·addVW(SB),NOSPLIT,$0