math: remove most 387 implementations

The Surface Pro X's 386 simulator is not completely faithful to a real 387.
The most egregious problem is that it computes Log2(8) as 2.9999999999999996,
but it has some other subtler problems as well. All the problems occur in
routines that we don't even bother with assembly for on amd64.
If the speed of Go code is OK on amd64 it should be OK on 386 too.
Just remove all the 386-only assembly functions.

This leaves Ceil, Floor, Trunc, Hypot, and Sqrt in 386 assembly,
all of which are also in assembly on amd64 and all of which pass
their tests on Surface Pro X.

Compared to amd64, the 386 port omits assembly for Min, Max, and Log.
It never had Min and Max, and this CL deletes Log because Log2 wasn't
even correct. (None of the other architectures have assembly Log either.)

Change-Id: I5eb6c61084467035269d4098a36001447b7a0601
Reviewed-on: https://go-review.googlesource.com/c/go/+/291229
Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

14 files changed, 45 insertions, 321 deletions

diff --git a/src/math/asin_386.s b/src/math/asin_386.s
deleted file mode 100644
index 7dab390623..0000000000
--- a/src/math/asin_386.s
+++ /dev/null
@@ -1,30 +0,0 @@
-// Copyright 2010 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"
-
-// func Asin(x float64) float64
-TEXT ·Asin(SB),NOSPLIT,$0
-	FMOVD   x+0(FP), F0  // F0=sin(x)
-	FMOVD   F0, F1       // F0=sin(x), F1=sin(x)
-	FMULD   F0, F0       // F0=sin(x)*sin(x), F1=sin(x)
-	FLD1                 // F0=1, F1=sin(x)*sin(x), F2=sin(x)
-	FSUBRDP F0, F1       // F0=1-sin(x)*sin(x) (=cos(x)*cos(x)), F1=sin(x)
-	FSQRT                // F0=cos(x), F1=sin(x)
-	FPATAN               // F0=arcsin(sin(x))=x
-	FMOVDP  F0, ret+8(FP)
-	RET
-
-// func Acos(x float64) float64
-TEXT ·Acos(SB),NOSPLIT,$0
-	FMOVD   x+0(FP), F0  // F0=cos(x)
-	FMOVD   F0, F1       // F0=cos(x), F1=cos(x)
-	FMULD   F0, F0       // F0=cos(x)*cos(x), F1=cos(x)
-	FLD1                 // F0=1, F1=cos(x)*cos(x), F2=cos(x)
-	FSUBRDP F0, F1       // F0=1-cos(x)*cos(x) (=sin(x)*sin(x)), F1=cos(x)
-	FSQRT                // F0=sin(x), F1=cos(x)
-	FXCHD   F0, F1       // F0=cos(x), F1=sin(x)
-	FPATAN               // F0=arccos(cos(x))=x
-	FMOVDP	F0, ret+8(FP)
-	RET
diff --git a/src/math/atan2_386.s b/src/math/atan2_386.s
deleted file mode 100644
index 90d211bf5b..0000000000
--- a/src/math/atan2_386.s
+++ /dev/null
@@ -1,13 +0,0 @@
-// Copyright 2010 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"
-
-// func Atan2(y, x float64) float64	// =atan(y/x)
-TEXT ·Atan2(SB),NOSPLIT,$0
-	FMOVD   y+0(FP), F0  // F0=y
-	FMOVD   x+8(FP), F0  // F0=x, F1=y
-	FPATAN               // F0=atan(F1/F0)
-	FMOVDP  F0, ret+16(FP)
-	RET
diff --git a/src/math/atan_386.s b/src/math/atan_386.s
deleted file mode 100644
index 43e79b92b6..0000000000
--- a/src/math/atan_386.s
+++ /dev/null
@@ -1,13 +0,0 @@
-// Copyright 2010 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"
-
-// func Atan(x float64) float64
-TEXT ·Atan(SB),NOSPLIT,$0
-	FMOVD   x+0(FP), F0  // F0=x
-	FLD1                 // F0=1, F1=x
-	FPATAN               // F0=atan(F1/F0)
-	FMOVDP  F0, ret+8(FP)
-	RET
diff --git a/src/math/exp2_386.s b/src/math/exp2_386.s
deleted file mode 100644
index d04cad6a55..0000000000
--- a/src/math/exp2_386.s
+++ /dev/null
@@ -1,40 +0,0 @@
-// Copyright 2010 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"
-
-// func Exp2(x float64) float64
-TEXT ·Exp2(SB),NOSPLIT,$0
-// test bits for not-finite
-	MOVL    x_hi+4(FP), AX
-	ANDL    $0x7ff00000, AX
-	CMPL    AX, $0x7ff00000
-	JEQ     not_finite
-	FMOVD   x+0(FP), F0   // F0=x
-	FMOVD   F0, F1        // F0=x, F1=x
-	FRNDINT               // F0=int(x), F1=x
-	FSUBD   F0, F1        // F0=int(x), F1=x-int(x)
-	FXCHD   F0, F1        // F0=x-int(x), F1=int(x)
-	F2XM1                 // F0=2**(x-int(x))-1, F1=int(x)
-	FLD1                  // F0=1, F1=2**(x-int(x))-1, F2=int(x)
-	FADDDP  F0, F1        // F0=2**(x-int(x)), F1=int(x)
-	FSCALE                // F0=2**x, F1=int(x)
-	FMOVDP  F0, F1        // F0=2**x
-	FMOVDP  F0, ret+8(FP)
-	RET
-not_finite:
-// test bits for -Inf
-	MOVL    x_hi+4(FP), BX
-	MOVL    x_lo+0(FP), CX
-	CMPL    BX, $0xfff00000
-	JNE     not_neginf
-	CMPL    CX, $0
-	JNE     not_neginf
-	MOVL    $0, ret_lo+8(FP)
-	MOVL    $0, ret_hi+12(FP)
-	RET
-not_neginf:
-	MOVL    CX, ret_lo+8(FP)
-	MOVL    BX, ret_hi+12(FP)
-	RET
diff --git a/src/math/expm1_386.s b/src/math/expm1_386.s
deleted file mode 100644
index d020296ca7..0000000000
--- a/src/math/expm1_386.s
+++ /dev/null
@@ -1,57 +0,0 @@
-// Copyright 2010 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"
-
-// func Expm1(x float64) float64
-TEXT ·Expm1(SB),NOSPLIT,$0
-	FLDLN2               // F0=log(2) = 1/log2(e) ~ 0.693147
-	FMOVD   x+0(FP), F0  // F0=x, F1=1/log2(e)
-	FABS                 // F0=|x|, F1=1/log2(e)
-	FUCOMPP F0, F1       // compare F0 to F1
-	FSTSW   AX
-	SAHF
-	JCC     use_exp      // jump if F0 >= F1
-	FLDL2E                // F0=log2(e)
-	FMULD   x+0(FP), F0   // F0=x*log2(e) (-1<F0<1)
-	F2XM1                 // F0=e**x-1 = 2**(x*log2(e))-1
-	FMOVDP  F0, ret+8(FP)
-	RET
-use_exp:
-// test bits for not-finite
-	MOVL    x_hi+4(FP), AX
-	ANDL    $0x7ff00000, AX
-	CMPL    AX, $0x7ff00000
-	JEQ     not_finite
-	FLDL2E                // F0=log2(e)
-	FMULD   x+0(FP), F0   // F0=x*log2(e)
-	FMOVD   F0, F1        // F0=x*log2(e), F1=x*log2(e)
-	FRNDINT               // F0=int(x*log2(e)), F1=x*log2(e)
-	FSUBD   F0, F1        // F0=int(x*log2(e)), F1=x*log2(e)-int(x*log2(e))
-	FXCHD   F0, F1        // F0=x*log2(e)-int(x*log2(e)), F1=int(x*log2(e))
-	F2XM1                 // F0=2**(x*log2(e)-int(x*log2(e)))-1, F1=int(x*log2(e))
-	FLD1                  // F0=1, F1=2**(x*log2(e)-int(x*log2(e)))-1, F2=int(x*log2(e))
-	FADDDP  F0, F1        // F0=2**(x*log2(e)-int(x*log2(e))), F1=int(x*log2(e))
-	FSCALE                // F0=e**x, F1=int(x*log2(e))
-	FMOVDP  F0, F1        // F0=e**x
-	FLD1                  // F0=1, F1=e**x
-	FSUBDP  F0, F1        // F0=e**x-1
-	FMOVDP  F0, ret+8(FP)
-	RET
-not_finite:
-// test bits for -Inf
-	MOVL    x_hi+4(FP), BX
-	MOVL    x_lo+0(FP), CX
-	CMPL    BX, $0xfff00000
-	JNE     not_neginf
-	CMPL    CX, $0
-	JNE     not_neginf
-	FLD1                 // F0=1
-	FCHS                 // F0=-1
-	FMOVDP  F0, ret+8(FP)
-	RET
-not_neginf:
-	MOVL    CX, ret_lo+8(FP)
-	MOVL    BX, ret_hi+12(FP)
-	RET
diff --git a/src/math/frexp_386.s b/src/math/frexp_386.s
deleted file mode 100644
index 832b435fe8..0000000000
--- a/src/math/frexp_386.s
+++ /dev/null
@@ -1,25 +0,0 @@
-// Copyright 2010 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"
-
-// func Frexp(f float64) (frac float64, exp int)
-TEXT ·Frexp(SB),NOSPLIT,$0
-	FMOVD   f+0(FP), F0   // F0=f
-	FXAM
-	FSTSW   AX
-	SAHF
-	JNP     nan_zero_inf
-	JCS     nan_zero_inf
-	FXTRACT               // F0=f (0<=f<1), F1=e
-	FMULD  $(0.5), F0     // F0=f (0.5<=f<1), F1=e
-	FMOVDP  F0, frac+8(FP)   // F0=e
-	FLD1                  // F0=1, F1=e
-	FADDDP  F0, F1        // F0=e+1
-	FMOVLP  F0, exp+16(FP)  // (int=int32)
-	RET
-nan_zero_inf:
-	FMOVDP  F0, frac+8(FP)   // F0=e
-	MOVL    $0, exp+16(FP)  // exp=0
-	RET
diff --git a/src/math/ldexp_386.s b/src/math/ldexp_386.s
deleted file mode 100644
index 6f67ae1d13..0000000000
--- a/src/math/ldexp_386.s
+++ /dev/null
@@ -1,14 +0,0 @@
-// Copyright 2010 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"
-
-// func Ldexp(frac float64, exp int) float64
-TEXT ·Ldexp(SB),NOSPLIT,$0
-	FMOVL   exp+8(FP), F0   // F0=exp
-	FMOVD   frac+0(FP), F0   // F0=frac, F1=e
-	FSCALE                // F0=x*2**e, F1=e
-	FMOVDP  F0, F1        // F0=x*2**e
-	FMOVDP  F0, ret+12(FP)
-	RET
diff --git a/src/math/log10_386.s b/src/math/log10_386.s
deleted file mode 100644
index 10eecd90e2..0000000000
--- a/src/math/log10_386.s
+++ /dev/null
@@ -1,21 +0,0 @@
-// Copyright 2010 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"
-
-// func Log10(x float64) float64
-TEXT ·Log10(SB),NOSPLIT,$0
-	FLDLG2               // F0=log10(2)
-	FMOVD   x+0(FP), F0  // F0=x, F1=log10(2)
-	FYL2X                // F0=log10(x)=log2(x)*log10(2)
-	FMOVDP  F0, ret+8(FP)
-	RET
-
-// func Log2(x float64) float64
-TEXT ·Log2(SB),NOSPLIT,$0
-	FLD1                 // F0=1
-	FMOVD   x+0(FP), F0  // F0=x, F1=1
-	FYL2X                // F0=log2(x)
-	FMOVDP  F0, ret+8(FP)
-	RET
diff --git a/src/math/log1p_386.s b/src/math/log1p_386.s
deleted file mode 100644
index 63b7e62283..0000000000
--- a/src/math/log1p_386.s
+++ /dev/null
@@ -1,27 +0,0 @@
-// Copyright 2010 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"
-
-// func Log1p(x float64) float64
-TEXT ·Log1p(SB),NOSPLIT,$0
-	FMOVD   $(2.928932188134524e-01), F0
-	FMOVD   x+0(FP), F0  // F0=x, F1=1-sqrt(2)/2 = 0.29289321881345247559915564
-	FABS                 // F0=|x|, F1=1-sqrt(2)/2
-	FUCOMPP F0, F1       // compare F0 to F1
-	FSTSW   AX
-	FLDLN2               // F0=log(2)
-	ANDW    $0x0100, AX
-	JEQ     use_fyl2x    // jump if F0 >= F1
-	FMOVD   x+0(FP), F0  // F0=x, F1=log(2)
-	FYL2XP1              // F0=log(1+x)=log2(1+x)*log(2)
-	FMOVDP  F0, ret+8(FP)
-	RET
-use_fyl2x:
-	FLD1                 // F0=1, F2=log(2)
-	FADDD   x+0(FP), F0  // F0=1+x, F1=log(2)
-	FYL2X                // F0=log(1+x)=log2(1+x)*log(2)
-	FMOVDP  F0, ret+8(FP)
-	RET
-
diff --git a/src/math/log_386.s b/src/math/log_386.s
deleted file mode 100644
index 0b64b507b2..0000000000
--- a/src/math/log_386.s
+++ /dev/null
@@ -1,13 +0,0 @@
-// Copyright 2010 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"
-
-// func Log(x float64) float64
-TEXT ·Log(SB),NOSPLIT,$0
-	FLDLN2               // F0=log(2)
-	FMOVD   x+0(FP), F0  // F0=x, F1=log(2)
-	FYL2X                // F0=log(x)=log2(x)*log(2)
-	FMOVDP  F0, ret+8(FP)
-	RET
diff --git a/src/math/mod_386.s b/src/math/mod_386.s
deleted file mode 100644
index 10ad98be3e..0000000000
--- a/src/math/mod_386.s
+++ /dev/null
@@ -1,17 +0,0 @@
-// Copyright 2010 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"
-
-// func Mod(x, y float64) float64
-TEXT ·Mod(SB),NOSPLIT,$0
-	FMOVD   y+8(FP), F0  // F0=y
-	FMOVD   x+0(FP), F0  // F0=x, F1=y
-	FPREM                // F0=reduced_x, F1=y
-	FSTSW   AX           // AX=status word
-	ANDW    $0x0400, AX
-	JNE     -3(PC)       // jump if reduction incomplete
-	FMOVDP  F0, F1       // F0=x-q*y
-	FMOVDP  F0, ret+16(FP)
-	RET
diff --git a/src/math/modf_386.s b/src/math/modf_386.s
deleted file mode 100644
index e9160735d3..0000000000
--- a/src/math/modf_386.s
+++ /dev/null
@@ -1,34 +0,0 @@
-// Copyright 2010 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"
-
-// func Modf(f float64) (int float64, frac float64)
-TEXT ·Modf(SB),NOSPLIT,$0
-	// special case for f == -0.0
-	MOVL f_hi+4(FP), DX	// high word
-	MOVL f_lo+0(FP), AX	// low word
-	CMPL DX, $(1<<31)	// beginning of -0.0
-	JNE notNegativeZero
-	CMPL AX, $0			// could be denormalized
-	JNE notNegativeZero
-	MOVL AX, int_lo+8(FP)
-	MOVL DX, int_hi+12(FP)
-	MOVL AX, frac_lo+16(FP)
-	MOVL DX, frac_hi+20(FP)
-	RET
-notNegativeZero:
-	FMOVD   f+0(FP), F0  // F0=f
-	FMOVD   F0, F1       // F0=f, F1=f
-	FSTCW   -2(SP)       // save old Control Word
-	MOVW    -2(SP), AX
-	ORW     $0x0c00, AX  // Rounding Control set to truncate
-	MOVW    AX, -4(SP)   // store new Control Word
-	FLDCW   -4(SP)       // load new Control Word
-	FRNDINT              // F0=trunc(f), F1=f
-	FLDCW   -2(SP)       // load old Control Word
-	FSUBD   F0, F1       // F0=trunc(f), F1=f-trunc(f)
-	FMOVDP  F0, int+8(FP)  // F0=f-trunc(f)
-	FMOVDP  F0, frac+16(FP)
-	RET
diff --git a/src/math/remainder_386.s b/src/math/remainder_386.s
deleted file mode 100644
index 318fa2c465..0000000000
--- a/src/math/remainder_386.s
+++ /dev/null
@@ -1,17 +0,0 @@
-// Copyright 2010 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"
-
-// func Remainder(x, y float64) float64
-TEXT ·Remainder(SB),NOSPLIT,$0
-	FMOVD   y+8(FP), F0  // F0=y
-	FMOVD   x+0(FP), F0  // F0=x, F1=y
-	FPREM1               // F0=reduced_x, F1=y
-	FSTSW   AX           // AX=status word
-	ANDW    $0x0400, AX
-	JNE     -3(PC)       // jump if reduction incomplete
-	FMOVDP  F0, F1       // F0=x-q*y
-	FMOVDP  F0, ret+16(FP)
-	RET
diff --git a/src/math/stubs_386.s b/src/math/stubs_386.s
index 92c8621523..bccb3edd11 100644
--- a/src/math/stubs_386.s
+++ b/src/math/stubs_386.s
@@ -4,12 +4,24 @@
 
 #include "textflag.h"
 
+TEXT ·Acos(SB), NOSPLIT, $0
+	JMP ·acos(SB)
+
 TEXT ·Acosh(SB), NOSPLIT, $0
 	JMP ·acosh(SB)
 
+TEXT ·Asin(SB), NOSPLIT, $0
+	JMP ·asin(SB)
+
 TEXT ·Asinh(SB), NOSPLIT, $0
 	JMP ·asinh(SB)
 
+TEXT ·Atan(SB), NOSPLIT, $0
+	JMP ·atan(SB)
+
+TEXT ·Atan2(SB), NOSPLIT, $0
+	JMP ·atan2(SB)
+
 TEXT ·Atanh(SB), NOSPLIT, $0
 	JMP ·atanh(SB)
 
@@ -31,15 +43,48 @@ TEXT ·Erfc(SB), NOSPLIT, $0
 TEXT ·Exp(SB), NOSPLIT, $0
 	JMP ·exp(SB)
 
+TEXT ·Exp2(SB), NOSPLIT, $0
+	JMP ·exp2(SB)
+
+TEXT ·Expm1(SB), NOSPLIT, $0
+	JMP ·expm1(SB)
+
+TEXT ·Frexp(SB), NOSPLIT, $0
+	JMP ·frexp(SB)
+
+TEXT ·Ldexp(SB), NOSPLIT, $0
+	JMP ·ldexp(SB)
+
+TEXT ·Log10(SB), NOSPLIT, $0
+	JMP ·log10(SB)
+
+TEXT ·Log2(SB), NOSPLIT, $0
+	JMP ·log2(SB)
+
+TEXT ·Log1p(SB), NOSPLIT, $0
+	JMP ·log1p(SB)
+
+TEXT ·Log(SB), NOSPLIT, $0
+	JMP ·log(SB)
+
 TEXT ·Max(SB), NOSPLIT, $0
 	JMP ·max(SB)
 
 TEXT ·Min(SB), NOSPLIT, $0
 	JMP ·min(SB)
 
+TEXT ·Mod(SB), NOSPLIT, $0
+	JMP ·mod(SB)
+
+TEXT ·Modf(SB), NOSPLIT, $0
+	JMP ·modf(SB)
+
 TEXT ·Pow(SB), NOSPLIT, $0
 	JMP ·pow(SB)
 
+TEXT ·Remainder(SB), NOSPLIT, $0
+	JMP ·remainder(SB)
+
 TEXT ·Sin(SB), NOSPLIT, $0
 	JMP ·sin(SB)