runtime: add tests for addrRanges.findSucc

This change adds a test suite for addrRanges.findSucc so we can change
the implementation more safely.

For #40191.

Change-Id: I14a834b6d54836cbc676eb0edb292ba6176705cc
Reviewed-on: https://go-review.googlesource.com/c/go/+/242678
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

src/runtime/export_test.go

@@ -785,6 +785,30 @@ func (a AddrRange) Equals(b AddrRange) bool {
 	return a == b
 }
 
+// AddrRanges is a wrapper around addrRanges for testing.
+type AddrRanges struct {
+	addrRanges
+}
+
+// MakeAddrRanges creates a new addrRanges populated with
+// the ranges in a.
+func MakeAddrRanges(a ...AddrRange) AddrRanges {
+	// Methods that manipulate the backing store of addrRanges.ranges should
+	// not be used on the result from this function (e.g. add) since they may
+	// trigger reallocation.
+	ranges := make([]addrRange, 0, len(a))
+	for _, r := range a {
+		ranges = append(ranges, r.addrRange)
+	}
+	return AddrRanges{addrRanges{ranges: ranges, sysStat: new(uint64)}}
+}
+
+// FindSucc returns the successor to base. See addrRanges.findSucc
+// for more details.
+func (a *AddrRanges) FindSucc(base uintptr) int {
+	return a.findSucc(base)
+}
+
 // BitRange represents a range over a bitmap.
 type BitRange struct {
 	I, N uint // bit index and length in bits

src/runtime/mranges_test.go

@@ -0,0 +1,172 @@
+// Copyright 2020 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 runtime_test
+
+import (
+	. "runtime"
+	"testing"
+)
+
+func TestAddrRangesFindSucc(t *testing.T) {
+	var large []AddrRange
+	for i := 0; i < 100; i++ {
+		large = append(large, MakeAddrRange(5+uintptr(i)*5, 5+uintptr(i)*5+3))
+	}
+
+	type testt struct {
+		name   string
+		base   uintptr
+		expect int
+		ranges []AddrRange
+	}
+	tests := []testt{
+		{
+			name:   "Empty",
+			base:   12,
+			expect: 0,
+			ranges: []AddrRange{},
+		},
+		{
+			name:   "OneBefore",
+			base:   12,
+			expect: 0,
+			ranges: []AddrRange{
+				MakeAddrRange(14, 16),
+			},
+		},
+		{
+			name:   "OneWithin",
+			base:   14,
+			expect: 1,
+			ranges: []AddrRange{
+				MakeAddrRange(14, 16),
+			},
+		},
+		{
+			name:   "OneAfterLimit",
+			base:   16,
+			expect: 1,
+			ranges: []AddrRange{
+				MakeAddrRange(14, 16),
+			},
+		},
+		{
+			name:   "OneAfter",
+			base:   17,
+			expect: 1,
+			ranges: []AddrRange{
+				MakeAddrRange(14, 16),
+			},
+		},
+		{
+			name:   "ThreeBefore",
+			base:   3,
+			expect: 0,
+			ranges: []AddrRange{
+				MakeAddrRange(6, 10),
+				MakeAddrRange(12, 16),
+				MakeAddrRange(19, 22),
+			},
+		},
+		{
+			name:   "ThreeAfter",
+			base:   24,
+			expect: 3,
+			ranges: []AddrRange{
+				MakeAddrRange(6, 10),
+				MakeAddrRange(12, 16),
+				MakeAddrRange(19, 22),
+			},
+		},
+		{
+			name:   "ThreeBetween",
+			base:   11,
+			expect: 1,
+			ranges: []AddrRange{
+				MakeAddrRange(6, 10),
+				MakeAddrRange(12, 16),
+				MakeAddrRange(19, 22),
+			},
+		},
+		{
+			name:   "ThreeWithin",
+			base:   9,
+			expect: 1,
+			ranges: []AddrRange{
+				MakeAddrRange(6, 10),
+				MakeAddrRange(12, 16),
+				MakeAddrRange(19, 22),
+			},
+		},
+		{
+			name:   "Zero",
+			base:   0,
+			expect: 1,
+			ranges: []AddrRange{
+				MakeAddrRange(0, 10),
+			},
+		},
+		{
+			name:   "Max",
+			base:   ^uintptr(0),
+			expect: 1,
+			ranges: []AddrRange{
+				MakeAddrRange(^uintptr(0)-5, ^uintptr(0)),
+			},
+		},
+		{
+			name:   "LargeBefore",
+			base:   2,
+			expect: 0,
+			ranges: large,
+		},
+		{
+			name:   "LargeAfter",
+			base:   5 + uintptr(len(large))*5 + 30,
+			expect: len(large),
+			ranges: large,
+		},
+		{
+			name:   "LargeBetweenLow",
+			base:   14,
+			expect: 2,
+			ranges: large,
+		},
+		{
+			name:   "LargeBetweenHigh",
+			base:   249,
+			expect: 49,
+			ranges: large,
+		},
+		{
+			name:   "LargeWithinLow",
+			base:   25,
+			expect: 5,
+			ranges: large,
+		},
+		{
+			name:   "LargeWithinHigh",
+			base:   396,
+			expect: 79,
+			ranges: large,
+		},
+		{
+			name:   "LargeWithinMiddle",
+			base:   250,
+			expect: 50,
+			ranges: large,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			a := MakeAddrRanges(test.ranges...)
+			i := a.FindSucc(test.base)
+			if i != test.expect {
+				t.Fatalf("expected %d, got %d", test.expect, i)
+			}
+		})
+	}
+}