go/src/pkg/math/modf_arm.s

// Copyright 2011 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.

TEXT ·Modf(SB),7,$0
	B ·modf(SB)
math: regularize build This will be nicer to the automatic tools. It requires a few more assembly stubs but fewer Go files. There are a few instances where it looks like there are new blobs of code, but they are just being copied out of deleted files. There is no new code here. Suppose you have a portable implementation for Sin and a 386-specific assembly one. The old way to do this was to write three files sin_decl.go func Sin(x float64) float64 // declaration only sin_386.s assembly implementation sin_port.go func Sin(x float64) float64 { ... } // pure-Go impl and then link in either sin_decl.go+sin_386.s or just sin_port.go. The Makefile actually did the magic of linking in only the _port.go files for those without assembly and only the _decl.go files for those with assembly, or at least some of that magic. The biggest problem with this, beyond being hard to explain to the build system, is that once you do explain it to the build system, godoc knows which of sin_port.go or sin_decl.go are involved on a given architecture, and it (correctly) ignores the other. That means you have to put identical doc comments in both files. The new approach, which is more like what we did in the later packages math/big and sync/atomic, is to have sin.go func Sin(x float64) float64 // decl only func sin(x float64) float64 {...} // pure-Go impl sin_386.s // assembly for Sin (ignores sin) sin_amd64.s // assembly for Sin: jmp sin sin_arm.s // assembly for Sin: jmp sin Once we abandon Makefiles we can put all the assembly stubs in one source file, so the number of files will actually go down. Chris asked whether the branches cost anything. Given that they are branching to pure-Go implementations that are not typically known for their speed, the single direct branch is not going to be noticeable. That is, it's on the slow path. An alternative would have been to preserve the old "only write assembly files when there's an implementation" and still have just one copy of the declaration of Sin (and thus one doc comment) by doing: sin.go func Sin(x float64) float64 { return sin(x) } sin_decl.go func sin(x float64) float64 // declaration only sin_386.s // assembly for sin sin_port.go func sin(x float64) float64 { portable code } In this version everyone would link in sin.go and then either sin_decl.go+sin_386.s or sin_port.go. This has an extra function call on all paths, including the "fast path" to get to assembly, and it triples the number of Go files involved compared to what I did in this CL. On the other hand you don't have to write assembly stubs. After starting down this path I decided that the assembly stubs were the easier approach. As for generating the assembly stubs on the fly, much of the goal here is to eliminate magic from the build process, so that zero-configuration tools like goinstall or the new go tool can handle this package. R=golang-dev, r, cw, iant, r CC=golang-dev https://golang.org/cl/5488057 2011-12-13 13:20:12 -07:00			`// Copyright 2011 The Go Authors. All rights reserved.`
math: 386 FPU functions sin, cos, tan, asin, acos, atan, exp, log, log10, floor, ceil, and fabs R=rsc CC=golang-dev https://golang.org/cl/189083 2010-01-15 14:21:36 -07:00			`// Use of this source code is governed by a BSD-style`
			`// license that can be found in the LICENSE file.`

math: regularize build This will be nicer to the automatic tools. It requires a few more assembly stubs but fewer Go files. There are a few instances where it looks like there are new blobs of code, but they are just being copied out of deleted files. There is no new code here. Suppose you have a portable implementation for Sin and a 386-specific assembly one. The old way to do this was to write three files sin_decl.go func Sin(x float64) float64 // declaration only sin_386.s assembly implementation sin_port.go func Sin(x float64) float64 { ... } // pure-Go impl and then link in either sin_decl.go+sin_386.s or just sin_port.go. The Makefile actually did the magic of linking in only the _port.go files for those without assembly and only the _decl.go files for those with assembly, or at least some of that magic. The biggest problem with this, beyond being hard to explain to the build system, is that once you do explain it to the build system, godoc knows which of sin_port.go or sin_decl.go are involved on a given architecture, and it (correctly) ignores the other. That means you have to put identical doc comments in both files. The new approach, which is more like what we did in the later packages math/big and sync/atomic, is to have sin.go func Sin(x float64) float64 // decl only func sin(x float64) float64 {...} // pure-Go impl sin_386.s // assembly for Sin (ignores sin) sin_amd64.s // assembly for Sin: jmp sin sin_arm.s // assembly for Sin: jmp sin Once we abandon Makefiles we can put all the assembly stubs in one source file, so the number of files will actually go down. Chris asked whether the branches cost anything. Given that they are branching to pure-Go implementations that are not typically known for their speed, the single direct branch is not going to be noticeable. That is, it's on the slow path. An alternative would have been to preserve the old "only write assembly files when there's an implementation" and still have just one copy of the declaration of Sin (and thus one doc comment) by doing: sin.go func Sin(x float64) float64 { return sin(x) } sin_decl.go func sin(x float64) float64 // declaration only sin_386.s // assembly for sin sin_port.go func sin(x float64) float64 { portable code } In this version everyone would link in sin.go and then either sin_decl.go+sin_386.s or sin_port.go. This has an extra function call on all paths, including the "fast path" to get to assembly, and it triples the number of Go files involved compared to what I did in this CL. On the other hand you don't have to write assembly stubs. After starting down this path I decided that the assembly stubs were the easier approach. As for generating the assembly stubs on the fly, much of the goal here is to eliminate magic from the build process, so that zero-configuration tools like goinstall or the new go tool can handle this package. R=golang-dev, r, cw, iant, r CC=golang-dev https://golang.org/cl/5488057 2011-12-13 13:20:12 -07:00			`TEXT ·Modf(SB),7,$0`
			`B ·modf(SB)`