math: use Trunc to implement Modf

By implementing Modf using Trunc, rather than the other way round,
we can get a significant performance improvement on platforms where
Trunc is implemented as an intrinsic.

Trunc is implemented as an intrinsic on ppc64x and arm64 so the assembly
implementations of Modf are no longer needed (the compiler can generate
very similar code that can now potentially be inlined).

GOAMD64=v1

goos: linux
goarch: amd64
pkg: math
cpu: 12th Gen Intel(R) Core(TM) i7-12700T
        │       sec/op       │    sec/op     vs base                │
Gamma            4.257n ± 0%    3.890n ± 0%   -8.61% (p=0.000 n=10)
Modf            1.6110n ± 0%   0.4243n ± 0%  -73.67% (p=0.000 n=10)
geomean          2.619n         1.285n       -50.94%

GOAMD64=v2

goos: linux
goarch: amd64
pkg: math
cpu: 12th Gen Intel(R) Core(TM) i7-12700T
        │       sec/op       │    sec/op     vs base                │
Gamma            4.100n ± 1%    3.717n ± 0%   -9.35% (p=0.000 n=10)
Modf            1.6070n ± 0%   0.2158n ± 1%  -86.57% (p=0.000 n=10)
geomean          2.567n        0.8957n       -65.11%

Change-Id: I689a560c344cf1d39ef002b540749bacc3179786
Reviewed-on: https://go-review.googlesource.com/c/go/+/694896
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@google.com>

0 files changed, 0 insertions, 0 deletions