cmd/compile: give "magic" code its own source file

This code is an eye sore to keep scrolling past in subr.go, so move it
out of the way.

Change-Id: I8eafc1725d868a4924ee7ca9b7738cce309f9eff
Reviewed-on: https://go-review.googlesource.com/20592Reviewed-by: Dave Cheney <dave@cheney.net>

src/cmd/compile/internal/gc/go.go

@@ -191,23 +191,6 @@ type Sig struct {
 	offset int32
 }
 
-// argument passing to/from
-// smagic and umagic
-type Magic struct {
-	W   int // input for both - width
-	S   int // output for both - shift
-	Bad int // output for both - unexpected failure
-
-	// magic multiplier for signed literal divisors
-	Sd int64 // input - literal divisor
-	Sm int64 // output - multiplier
-
-	// magic multiplier for unsigned literal divisors
-	Ud uint64 // input - literal divisor
-	Um uint64 // output - multiplier
-	Ua int    // output - adder
-}
-
 // note this is the runtime representation
 // of the compilers arrays.
 //

src/cmd/compile/internal/gc/magic.go

+// Copyright 2009 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.
+
+package gc
+
+// Transmogrify slow integer division into fast multiplication using magic.
+
+// argument passing to/from
+// smagic and umagic
+type Magic struct {
+	W   int // input for both - width
+	S   int // output for both - shift
+	Bad int // output for both - unexpected failure
+
+	// magic multiplier for signed literal divisors
+	Sd int64 // input - literal divisor
+	Sm int64 // output - multiplier
+
+	// magic multiplier for unsigned literal divisors
+	Ud uint64 // input - literal divisor
+	Um uint64 // output - multiplier
+	Ua int    // output - adder
+}
+
+// magic number for signed division
+// see hacker's delight chapter 10
+func Smagic(m *Magic) {
+	var mask uint64
+
+	m.Bad = 0
+	switch m.W {
+	default:
+		m.Bad = 1
+		return
+
+	case 8:
+		mask = 0xff
+
+	case 16:
+		mask = 0xffff
+
+	case 32:
+		mask = 0xffffffff
+
+	case 64:
+		mask = 0xffffffffffffffff
+	}
+
+	two31 := mask ^ (mask >> 1)
+
+	p := m.W - 1
+	ad := uint64(m.Sd)
+	if m.Sd < 0 {
+		ad = -uint64(m.Sd)
+	}
+
+	// bad denominators
+	if ad == 0 || ad == 1 || ad == two31 {
+		m.Bad = 1
+		return
+	}
+
+	t := two31
+	ad &= mask
+
+	anc := t - 1 - t%ad
+	anc &= mask
+
+	q1 := two31 / anc
+	r1 := two31 - q1*anc
+	q1 &= mask
+	r1 &= mask
+
+	q2 := two31 / ad
+	r2 := two31 - q2*ad
+	q2 &= mask
+	r2 &= mask
+
+	var delta uint64
+	for {
+		p++
+		q1 <<= 1
+		r1 <<= 1
+		q1 &= mask
+		r1 &= mask
+		if r1 >= anc {
+			q1++
+			r1 -= anc
+			q1 &= mask
+			r1 &= mask
+		}
+
+		q2 <<= 1
+		r2 <<= 1
+		q2 &= mask
+		r2 &= mask
+		if r2 >= ad {
+			q2++
+			r2 -= ad
+			q2 &= mask
+			r2 &= mask
+		}
+
+		delta = ad - r2
+		delta &= mask
+		if q1 < delta || (q1 == delta && r1 == 0) {
+			continue
+		}
+
+		break
+	}
+
+	m.Sm = int64(q2 + 1)
+	if uint64(m.Sm)&two31 != 0 {
+		m.Sm |= ^int64(mask)
+	}
+	m.S = p - m.W
+}
+
+// magic number for unsigned division
+// see hacker's delight chapter 10
+func Umagic(m *Magic) {
+	var mask uint64
+
+	m.Bad = 0
+	m.Ua = 0
+
+	switch m.W {
+	default:
+		m.Bad = 1
+		return
+
+	case 8:
+		mask = 0xff
+
+	case 16:
+		mask = 0xffff
+
+	case 32:
+		mask = 0xffffffff
+
+	case 64:
+		mask = 0xffffffffffffffff
+	}
+
+	two31 := mask ^ (mask >> 1)
+
+	m.Ud &= mask
+	if m.Ud == 0 || m.Ud == two31 {
+		m.Bad = 1
+		return
+	}
+
+	nc := mask - (-m.Ud&mask)%m.Ud
+	p := m.W - 1
+
+	q1 := two31 / nc
+	r1 := two31 - q1*nc
+	q1 &= mask
+	r1 &= mask
+
+	q2 := (two31 - 1) / m.Ud
+	r2 := (two31 - 1) - q2*m.Ud
+	q2 &= mask
+	r2 &= mask
+
+	var delta uint64
+	for {
+		p++
+		if r1 >= nc-r1 {
+			q1 <<= 1
+			q1++
+			r1 <<= 1
+			r1 -= nc
+		} else {
+			q1 <<= 1
+			r1 <<= 1
+		}
+
+		q1 &= mask
+		r1 &= mask
+		if r2+1 >= m.Ud-r2 {
+			if q2 >= two31-1 {
+				m.Ua = 1
+			}
+
+			q2 <<= 1
+			q2++
+			r2 <<= 1
+			r2++
+			r2 -= m.Ud
+		} else {
+			if q2 >= two31 {
+				m.Ua = 1
+			}
+
+			q2 <<= 1
+			r2 <<= 1
+			r2++
+		}
+
+		q2 &= mask
+		r2 &= mask
+
+		delta = m.Ud - 1 - r2
+		delta &= mask
+
+		if p < m.W+m.W {
+			if q1 < delta || (q1 == delta && r1 == 0) {
+				continue
+			}
+		}
+
+		break
+	}
+
+	m.Um = q2 + 1
+	m.S = p - m.W
+}

src/cmd/compile/internal/gc/subr.go

@@ -2286,202 +2286,6 @@ func tounsigned(t *Type) *Type {
 	return t
 }
 
-// magic number for signed division
-// see hacker's delight chapter 10
-func Smagic(m *Magic) {
-	var mask uint64
-
-	m.Bad = 0
-	switch m.W {
-	default:
-		m.Bad = 1
-		return
-
-	case 8:
-		mask = 0xff
-
-	case 16:
-		mask = 0xffff
-
-	case 32:
-		mask = 0xffffffff
-
-	case 64:
-		mask = 0xffffffffffffffff
-	}
-
-	two31 := mask ^ (mask >> 1)
-
-	p := m.W - 1
-	ad := uint64(m.Sd)
-	if m.Sd < 0 {
-		ad = -uint64(m.Sd)
-	}
-
-	// bad denominators
-	if ad == 0 || ad == 1 || ad == two31 {
-		m.Bad = 1
-		return
-	}
-
-	t := two31
-	ad &= mask
-
-	anc := t - 1 - t%ad
-	anc &= mask
-
-	q1 := two31 / anc
-	r1 := two31 - q1*anc
-	q1 &= mask
-	r1 &= mask
-
-	q2 := two31 / ad
-	r2 := two31 - q2*ad
-	q2 &= mask
-	r2 &= mask
-
-	var delta uint64
-	for {
-		p++
-		q1 <<= 1
-		r1 <<= 1
-		q1 &= mask
-		r1 &= mask
-		if r1 >= anc {
-			q1++
-			r1 -= anc
-			q1 &= mask
-			r1 &= mask
-		}
-
-		q2 <<= 1
-		r2 <<= 1
-		q2 &= mask
-		r2 &= mask
-		if r2 >= ad {
-			q2++
-			r2 -= ad
-			q2 &= mask
-			r2 &= mask
-		}
-
-		delta = ad - r2
-		delta &= mask
-		if q1 < delta || (q1 == delta && r1 == 0) {
-			continue
-		}
-
-		break
-	}
-
-	m.Sm = int64(q2 + 1)
-	if uint64(m.Sm)&two31 != 0 {
-		m.Sm |= ^int64(mask)
-	}
-	m.S = p - m.W
-}
-
-// magic number for unsigned division
-// see hacker's delight chapter 10
-func Umagic(m *Magic) {
-	var mask uint64
-
-	m.Bad = 0
-	m.Ua = 0
-
-	switch m.W {
-	default:
-		m.Bad = 1
-		return
-
-	case 8:
-		mask = 0xff
-
-	case 16:
-		mask = 0xffff
-
-	case 32:
-		mask = 0xffffffff
-
-	case 64:
-		mask = 0xffffffffffffffff
-	}
-
-	two31 := mask ^ (mask >> 1)
-
-	m.Ud &= mask
-	if m.Ud == 0 || m.Ud == two31 {
-		m.Bad = 1
-		return
-	}
-
-	nc := mask - (-m.Ud&mask)%m.Ud
-	p := m.W - 1
-
-	q1 := two31 / nc
-	r1 := two31 - q1*nc
-	q1 &= mask
-	r1 &= mask
-
-	q2 := (two31 - 1) / m.Ud
-	r2 := (two31 - 1) - q2*m.Ud
-	q2 &= mask
-	r2 &= mask
-
-	var delta uint64
-	for {
-		p++
-		if r1 >= nc-r1 {
-			q1 <<= 1
-			q1++
-			r1 <<= 1
-			r1 -= nc
-		} else {
-			q1 <<= 1
-			r1 <<= 1
-		}
-
-		q1 &= mask
-		r1 &= mask
-		if r2+1 >= m.Ud-r2 {
-			if q2 >= two31-1 {
-				m.Ua = 1
-			}
-
-			q2 <<= 1
-			q2++
-			r2 <<= 1
-			r2++
-			r2 -= m.Ud
-		} else {
-			if q2 >= two31 {
-				m.Ua = 1
-			}
-
-			q2 <<= 1
-			r2 <<= 1
-			r2++
-		}
-
-		q2 &= mask
-		r2 &= mask
-
-		delta = m.Ud - 1 - r2
-		delta &= mask
-
-		if p < m.W+m.W {
-			if q1 < delta || (q1 == delta && r1 == 0) {
-				continue
-			}
-		}
-
-		break
-	}
-
-	m.Um = q2 + 1
-	m.S = p - m.W
-}
-
 func ngotype(n *Node) *Sym {
 	if n.Type != nil {
 		return typenamesym(n.Type)