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internal/radix51: Use BMI2 to accelerate FieldElement.Square 

```
name      old time/op  new time/op  delta
Square-8  29.0ns ± 2%  26.5ns ± 0%  -8.63%  (p=0.008 n=5+5)
```
This commit is contained in:
Yawning Angel 2021-02-09 14:46:57 +00:00
parent a8296fe54a
commit dbb69fe162
2 changed files with 87 additions and 3 deletions
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6
internal/radix51/fe_amd64.go
View File

@ -22,12 +22,16 @@ var useBMI2 bool
func feMulAmd64(out, a, b *FieldElement, useBMI2 bool)
//go:noescape
func feSquare(out, x *FieldElement)
func feSquareAmd64(out, x *FieldElement, useBMI2 bool)
func feMul(out, a, b *FieldElement) {
feMulAmd64(out, a, b, useBMI2)
}
func feSquare(out, x *FieldElement) {
feSquareAmd64(out, x, useBMI2)
}
func init() {
useBMI2 = cpu.Initialized && cpu.X86.HasBMI2
}

84
internal/radix51/fe_amd64.s
View File

@ -327,10 +327,89 @@ mul_reduce:
MOVQ R14, 32(DI)
RET
// func feSquare(out, x *FieldElement)
TEXT ·feSquare(SB), NOSPLIT|NOFRAME, $0-16
// func feSquareAmd64(out, x *FieldElement, useBMI2 bool)
TEXT ·feSquareAmd64(SB), NOSPLIT|NOFRAME, $0-17
MOVQ x+8(FP), BX
// Pick the appropriate implementation, based on if the caller thinks
// BMI2 is supported or not.
MOVBQZX useBMI2+16(FP), DX
TESTQ DX, DX
JZ square_vanilla
// This codepath uses BMI2 to shave off a number of instructions,
// for a slight performance gain.
// r0 = a0*a0
// r1 = 2*a0*a1
// r2 = 2*a0*a2
// r3 = 2*a0*a3
// r4 = 2*a0*a4
MOVQ 0(BX), DX // rdx <- a0
MULXQ DX, SI, BP // r00, r01 <- a0*a0
SHLQ $1, DX // rdx *= 2 (d0 = 2*a0)
MULXQ 8(BX), R8, R9 // r10, r11 <- d0*a1
MULXQ 16(BX), R10, R11 // r20, r21 <- d0*a2
MULXQ 24(BX), R12, R13 // r30, r31 <- d0*a3
MULXQ 32(BX), R14, R15 // r40, r41 <- d0*a4
// r2 += a1*a1
// r3 += 2*a1*a2
// r4 += 2*a1*a3
MOVQ 8(BX), DX // rdx <- a1
MULXQ DX, AX, DI // rdi, rax = a1*a1
ADDQ AX, R10 // r20 += rax
ADCQ DI, R11 // r21 += rdi + cf
SHLQ $1, DX // rdx *= 2 (d1 = 2*a1)
MULXQ 16(BX), AX, DI // rdi, rax = d1*a2
ADDQ AX, R12 // r30 += rax
ADCQ DI, R13 // r31 += rdi + cf
MULXQ 24(BX), AX, DI // rdi, rax = d1*a3
ADDQ AX, R14 // r40 += rax
ADCQ DI, R15 // r41 += rdi + cf
IMUL3Q $19, DX, DX // rdx *= 19 (d1_38 = 2*19*a1)
MULXQ 32(BX), AX, DI // rdi, rax = d1_38*a4
ADDQ AX, SI // r00 += rax
ADCQ DI, BP // r01 += rdi + cf
// r4 += a2*a2
// r0 += 2*19*a2*a3
// r1 += 2*19*a2*a4
MOVQ 16(BX), DX // rdx <- a2
MULXQ DX, AX, DI // rdi, rax = a2*a2
ADDQ AX, R14 // r40 += rax
ADCQ DI, R15 // r41 += rdi + cf
IMUL3Q $38, DX, DX // dx *= 2*19 (d2_38 = 2*19*a2)
MULXQ 24(BX), AX, DI // rdi, rax = d2_38*a3
ADDQ AX, SI // r00 += rax
ADCQ DI, BP // r01 += rdi + cf
MULXQ 32(BX), AX, DI // rdi, rax = d2_38*a4
ADDQ AX, R8 // r10 += rax
ADCQ DI, R9 // r11 += rdi + cf
// r1 += 19*a3*a3
// r2 += 2*19*a4*a3
MOVQ 24(BX), DX // rdx <- a3
IMUL3Q $19, DX, DX // dx *= 19 (d3_19 = 19*a3)
MULXQ 24(BX), AX, DI // rdi, rax = d3_19*a3
ADDQ AX, R8 // r10 += rax
ADCQ DI, R9 // r11 += rdi + cf
SHLQ $1, DX // rdx *= 2 (d3_38 = 2*19*a3)
MULXQ 32(BX), AX, DI // rdi, rax = d3_38*a4
ADDQ AX, R10 // r20 += rax
ADCQ DI, R11 // r21 += rdi + cf
// r3 += 19*a4*a4
MOVQ 32(BX), DX // rdx <- a4
IMUL3Q $19, DX, DX // dx *= 19 (d4_19 = 19*a4)
MULXQ 32(BX), AX, DI // rdi, rax = d4_19*a4
ADDQ AX, R12 // r30 += rax
ADCQ DI, R13 // r31 += rdi + cf
JMP square_reduce
square_vanilla:
// r0 = x0*x0 + x1*38*x4 + x2*38*x3
MOVQ 0(BX), AX
MULQ 0(BX)
@ -423,6 +502,7 @@ TEXT ·feSquare(SB), NOSPLIT|NOFRAME, $0-16
ADDQ AX, R14
ADCQ DX, R15
square_reduce:
// Reduce
reduce64()