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math: add round assembly implementations on riscv64

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This CL reapplies CL 504737 and adds integer precision
limitation check, since CL 504737 only checks whether
floating point number is +-Inf or NaN.

This CL is also ~7% faster than CL 504737.

Updates #68322

goos: linux
goarch: riscv64
pkg: math
            │ math.old.bench │           math.new.bench            │
            │     sec/op     │   sec/op     vs base                │
Ceil             54.09n ± 0%   18.72n ± 0%  -65.39% (p=0.000 n=10)
Floor            40.72n ± 0%   18.72n ± 0%  -54.03% (p=0.000 n=10)
Round            20.73n ± 0%   20.73n ± 0%        ~ (p=1.000 n=10)
RoundToEven      24.07n ± 0%   24.07n ± 0%        ~ (p=1.000 n=10)
Trunc            38.72n ± 0%   18.72n ± 0%  -51.65% (p=0.000 n=10)
geomean          33.56n        20.09n       -40.13%

Change-Id: I06cfe2cb9e2535cd705d40b6650a7e71fedd906c
Reviewed-on: https://go-review.googlesource.com/c/go/+/600075
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Joel Sing <joel@sing.id.au>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This commit is contained in:
Meng Zhuo 2024-07-22 15:53:37 +08:00 committed by Meng Zhuo
parent 2982253c42
commit 90391c2e8a
3 changed files with 50 additions and 2 deletions
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2
src/math/floor_asm.go
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@ -2,7 +2,7 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build 386 || amd64 || arm64 || ppc64 || ppc64le || s390x || wasm
//go:build 386 || amd64 || arm64 || ppc64 || ppc64le || riscv64 || s390x || wasm
package math

2
src/math/floor_noasm.go
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@ -2,7 +2,7 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build !386 && !amd64 && !arm64 && !ppc64 && !ppc64le && !s390x && !wasm
//go:build !386 && !amd64 && !arm64 && !ppc64 && !ppc64le && !riscv64 && !s390x && !wasm
package math

48
src/math/floor_riscv64.s Normal file
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@ -0,0 +1,48 @@
// Copyright 2024 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.
#include "textflag.h"
// RISC-V offered floating-point (FP) rounding by FP conversion instructions (FCVT)
// with rounding mode field.
// As Go spec expects FP rounding result in FP, we have to use FCVT integer
// back to FP (fp -> int -> fp).
// RISC-V only set Inexact flag during invalid FP-integer conversion without changing any data,
// on the other hand, RISC-V sets out of integer represent range yet valid FP into NaN.
// When it comes to integer-FP conversion, invalid FP like NaN, +-Inf will be
// converted into the closest valid FP, for example:
//
// `Floor(-Inf) -> int64(0x7fffffffffffffff) -> float64(9.22e+18)`
// `Floor(18446744073709549568.0) -> int64(0x7fffffffffffffff) -> float64(9.22e+18)`
//
// This ISA conversion limitation requires we skip all invalid or out of range FP
// before any normal rounding operations.
#define ROUNDFN(NAME, MODE) \
TEXT NAME(SB),NOSPLIT,$0; \
MOVD x+0(FP), F10; \
FMVXD F10, X10; \
/* Drop all fraction bits */;\
SRL $52, X10, X12; \
/* Remove sign bit */; \
AND $0x7FF, X12, X12;\
/* Return either input is +-Inf, NaN(0x7FF) or out of precision limitation */;\
/* 1023: bias of exponent, [-2^53, 2^53]: exactly integer represent range */;\
MOV $1023+53, X11; \
BLTU X11, X12, 4(PC);\
FCVTLD.MODE F10, X11; \
FCVTDL X11, F11; \
/* RISC-V rounds negative values to +0, restore original sign */;\
FSGNJD F10, F11, F10; \
MOVD F10, ret+8(FP); \
RET
// func archFloor(x float64) float64
ROUNDFN(·archFloor, RDN)
// func archCeil(x float64) float64
ROUNDFN(·archCeil, RUP)
// func archTrunc(x float64) float64
ROUNDFN(·archTrunc, RTZ)