index/suffixarray: add 32-bit implementation

The original index/suffixarray used 32-bit ints on 64-bit machines,
because that's what 'int' meant in Go at the time. When we changed
the meaning of int, that doubled the space overhead of suffix arrays
for all uses, even though the vast majority of them describe less
than 2 GB of text.

The space overhead of a suffix array compared to the text is not
insignificant: there's a big difference for many uses between 4X and 8X.

This CL adjusts names in qsufsort.go so that a global search and
replace s/32/64/g produces a working 64-bit implementation,
and then it modifies suffixarray.go to choose between the 32-bit
and 64-bit implementation as appropriate depending on the input size.
The 64-bit implementation is generated by 'go generate'.

This CL also restructures the benchmarks, to test different
input sizes, different input texts, and 32-bit vs 64-bit.

The serialized form uses varint-encoded numbers and is unchanged,
so on-disk suffix arrays written by older versions of Go will be
readable by this version, and vice versa.

The 32-bit version runs a up to 17% faster than the 64-bit version
on real inputs, but more importantly it uses 50% less memory.

I have a followup CL that also implements a faster algorithm
on top of these improvements, but these are a good first step.

name                                  64-bit speed   32-bit speed    delta
New/text=opticks/size=100K/bits=*-12  4.44MB/s ± 0%  4.64MB/s ± 0%   +4.41%  (p=0.008 n=5+5)
New/text=opticks/size=500K/bits=*-12  3.70MB/s ± 1%  3.82MB/s ± 0%   +3.30%  (p=0.008 n=5+5)
New/text=go/size=100K/bits=*-12       4.40MB/s ± 0%  4.61MB/s ± 0%   +4.82%  (p=0.008 n=5+5)
New/text=go/size=500K/bits=*-12       3.66MB/s ± 0%  3.77MB/s ± 0%   +3.01%  (p=0.016 n=4+5)
New/text=go/size=1M/bits=*-12         3.29MB/s ± 0%  3.55MB/s ± 0%   +7.90%  (p=0.016 n=5+4)
New/text=go/size=5M/bits=*-12         2.25MB/s ± 1%  2.65MB/s ± 0%  +17.81%  (p=0.008 n=5+5)
New/text=go/size=10M/bits=*-12        1.82MB/s ± 0%  2.09MB/s ± 1%  +14.36%  (p=0.008 n=5+5)
New/text=go/size=50M/bits=*-12        1.35MB/s ± 0%  1.51MB/s ± 1%  +12.33%  (p=0.008 n=5+5)
New/text=zero/size=100K/bits=*-12     3.42MB/s ± 0%  3.32MB/s ± 0%   -2.74%  (p=0.000 n=5+4)
New/text=zero/size=500K/bits=*-12     3.00MB/s ± 1%  2.97MB/s ± 0%   -1.13%  (p=0.016 n=5+4)
New/text=zero/size=1M/bits=*-12       2.81MB/s ± 0%  2.78MB/s ± 2%     ~     (p=0.167 n=5+5)
New/text=zero/size=5M/bits=*-12       2.46MB/s ± 0%  2.53MB/s ± 0%   +3.18%  (p=0.008 n=5+5)
New/text=zero/size=10M/bits=*-12      2.35MB/s ± 0%  2.42MB/s ± 0%   +2.98%  (p=0.016 n=4+5)
New/text=zero/size=50M/bits=*-12      2.12MB/s ± 0%  2.18MB/s ± 0%   +3.02%  (p=0.008 n=5+5)
New/text=rand/size=100K/bits=*-12     6.98MB/s ± 0%  7.22MB/s ± 0%   +3.38%  (p=0.016 n=4+5)
New/text=rand/size=500K/bits=*-12     5.53MB/s ± 0%  5.64MB/s ± 0%   +1.92%  (p=0.008 n=5+5)
New/text=rand/size=1M/bits=*-12       4.62MB/s ± 1%  5.06MB/s ± 0%   +9.61%  (p=0.008 n=5+5)
New/text=rand/size=5M/bits=*-12       3.09MB/s ± 0%  3.43MB/s ± 0%  +10.94%  (p=0.016 n=4+5)
New/text=rand/size=10M/bits=*-12      2.68MB/s ± 0%  2.95MB/s ± 0%  +10.39%  (p=0.008 n=5+5)
New/text=rand/size=50M/bits=*-12      1.92MB/s ± 0%  2.06MB/s ± 1%   +7.41%  (p=0.008 n=5+5)
SaveRestore/bits=*-12                  243MB/s ± 1%   259MB/s ± 0%   +6.68%  (p=0.000 n=9+10)

name                               64-bit alloc/op  32-bit alloc/op  delta
New/text=opticks/size=100K/bits=*-12    1.62MB ± 0%    0.81MB ± 0%  -50.00%  (p=0.000 n=5+4)
New/text=opticks/size=500K/bits=*-12    8.07MB ± 0%    4.04MB ± 0%  -49.89%  (p=0.008 n=5+5)
New/text=go/size=100K/bits=*-12         1.62MB ± 0%    0.81MB ± 0%  -50.00%  (p=0.008 n=5+5)
New/text=go/size=500K/bits=*-12         8.07MB ± 0%    4.04MB ± 0%  -49.89%  (p=0.029 n=4+4)
New/text=go/size=1M/bits=*-12           16.1MB ± 0%     8.1MB ± 0%  -49.95%  (p=0.008 n=5+5)
New/text=go/size=5M/bits=*-12           80.3MB ± 0%    40.2MB ± 0%     ~     (p=0.079 n=4+5)
New/text=go/size=10M/bits=*-12           160MB ± 0%      80MB ± 0%  -50.00%  (p=0.008 n=5+5)
New/text=go/size=50M/bits=*-12           805MB ± 0%     402MB ± 0%  -50.06%  (p=0.029 n=4+4)
New/text=zero/size=100K/bits=*-12       3.02MB ± 0%    1.46MB ± 0%     ~     (p=0.079 n=4+5)
New/text=zero/size=500K/bits=*-12       19.7MB ± 0%     8.7MB ± 0%  -55.98%  (p=0.008 n=5+5)
New/text=zero/size=1M/bits=*-12         39.0MB ± 0%    19.7MB ± 0%  -49.60%  (p=0.000 n=5+4)
New/text=zero/size=5M/bits=*-12          169MB ± 0%      85MB ± 0%  -49.46%  (p=0.029 n=4+4)
New/text=zero/size=10M/bits=*-12         333MB ± 0%     169MB ± 0%  -49.43%  (p=0.000 n=5+4)
New/text=zero/size=50M/bits=*-12        1.63GB ± 0%    0.74GB ± 0%  -54.61%  (p=0.008 n=5+5)
New/text=rand/size=100K/bits=*-12       1.61MB ± 0%    0.81MB ± 0%  -50.00%  (p=0.000 n=5+4)
New/text=rand/size=500K/bits=*-12       8.07MB ± 0%    4.04MB ± 0%  -49.89%  (p=0.000 n=5+4)
New/text=rand/size=1M/bits=*-12         16.1MB ± 0%     8.1MB ± 0%  -49.95%  (p=0.029 n=4+4)
New/text=rand/size=5M/bits=*-12         80.7MB ± 0%    40.3MB ± 0%  -50.06%  (p=0.008 n=5+5)
New/text=rand/size=10M/bits=*-12         161MB ± 0%      81MB ± 0%  -50.03%  (p=0.008 n=5+5)
New/text=rand/size=50M/bits=*-12         806MB ± 0%     403MB ± 0%  -50.00%  (p=0.016 n=4+5)
SaveRestore/bits=*-12                   9.47MB ± 0%    5.28MB ± 0%  -44.29%  (p=0.000 n=9+8)

https://perf.golang.org/search?q=upload:20190126.1+|+bits:64+vs+bits:32

Fixes #6816.

Change-Id: Ied2fbea519a202ecc43719debcd233344ce38847
Reviewed-on: https://go-review.googlesource.com/c/go/+/174097
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

5 files changed, 525 insertions, 84 deletions

diff --git a/src/index/suffixarray/gen64.go b/src/index/suffixarray/gen64.go
new file mode 100644
index 0000000000..4f0e35e227
--- /dev/null
+++ b/src/index/suffixarray/gen64.go
@@ -0,0 +1,31 @@
+// Copyright 2019 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.
+
+// +build ignore
+
+// Gen64 generates qsufsort64.go from qsufsort.go by s/32/64/g.
+package main
+
+import (
+	"bytes"
+	"io/ioutil"
+	"log"
+)
+
+func main() {
+	log.SetPrefix("gen64: ")
+	log.SetFlags(0)
+
+	data, err := ioutil.ReadFile("qsufsort.go")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	data = bytes.Replace(data, []byte("\n\n"), []byte("\n\n// Code generated by gen64.go; DO NOT EDIT.\n//go:generate go run gen64.go\n\n"), 1)
+	data = bytes.Replace(data, []byte("32"), []byte("64"), -1)
+
+	if err := ioutil.WriteFile("qsufsort64.go", data, 0666); err != nil {
+		log.Fatal(err)
+	}
+}
diff --git a/src/index/suffixarray/qsufsort.go b/src/index/suffixarray/qsufsort.go
index 9c36a98f82..71aae02c0a 100644
--- a/src/index/suffixarray/qsufsort.go
+++ b/src/index/suffixarray/qsufsort.go
@@ -24,26 +24,28 @@
 
 package suffixarray
 
-import "sort"
+import (
+	"sort"
+)
 
-func qsufsort(data []byte) []int {
+func qsufsort32(data []byte) []int32 {
 	// initial sorting by first byte of suffix
-	sa := sortedByFirstByte(data)
+	sa := sortedByFirstByte32(data)
 	if len(sa) < 2 {
 		return sa
 	}
 	// initialize the group lookup table
 	// this becomes the inverse of the suffix array when all groups are sorted
-	inv := initGroups(sa, data)
+	inv := initGroups32(sa, data)
 
 	// the index starts 1-ordered
-	sufSortable := &suffixSortable{sa: sa, inv: inv, h: 1}
+	sufSortable := &suffixSortable32{sa: sa, inv: inv, h: 1}
 
-	for sa[0] > -len(sa) { // until all suffixes are one big sorted group
+	for sa[0] > -int32(len(sa)) { // until all suffixes are one big sorted group
 		// The suffixes are h-ordered, make them 2*h-ordered
-		pi := 0 // pi is first position of first group
-		sl := 0 // sl is negated length of sorted groups
-		for pi < len(sa) {
+		pi := int32(0) // pi is first position of first group
+		sl := int32(0) // sl is negated length of sorted groups
+		for pi < int32(len(sa)) {
 			if s := sa[pi]; s < 0 { // if pi starts sorted group
 				pi -= s // skip over sorted group
 				sl += s // add negated length to sl
@@ -67,12 +69,12 @@ func qsufsort(data []byte) []int {
 	}
 
 	for i := range sa { // reconstruct suffix array from inverse
-		sa[inv[i]] = i
+		sa[inv[i]] = int32(i)
 	}
 	return sa
 }
 
-func sortedByFirstByte(data []byte) []int {
+func sortedByFirstByte32(data []byte) []int32 {
 	// total byte counts
 	var count [256]int
 	for _, b := range data {
@@ -84,20 +86,20 @@ func sortedByFirstByte(data []byte) []int {
 		count[b], sum = sum, count[b]+sum
 	}
 	// iterate through bytes, placing index into the correct spot in sa
-	sa := make([]int, len(data))
+	sa := make([]int32, len(data))
 	for i, b := range data {
-		sa[count[b]] = i
+		sa[count[b]] = int32(i)
 		count[b]++
 	}
 	return sa
 }
 
-func initGroups(sa []int, data []byte) []int {
+func initGroups32(sa []int32, data []byte) []int32 {
 	// label contiguous same-letter groups with the same group number
-	inv := make([]int, len(data))
-	prevGroup := len(sa) - 1
+	inv := make([]int32, len(data))
+	prevGroup := int32(len(sa)) - 1
 	groupByte := data[sa[prevGroup]]
-	for i := len(sa) - 1; i >= 0; i-- {
+	for i := int32(len(sa)) - 1; i >= 0; i-- {
 		if b := data[sa[i]]; b < groupByte {
 			if prevGroup == i+1 {
 				sa[i+1] = -1
@@ -114,13 +116,13 @@ func initGroups(sa []int, data []byte) []int {
 	// This is necessary to ensure the suffix "a" is before "aba"
 	// when using a potentially unstable sort.
 	lastByte := data[len(data)-1]
-	s := -1
+	s := int32(-1)
 	for i := range sa {
 		if sa[i] >= 0 {
 			if data[sa[i]] == lastByte && s == -1 {
-				s = i
+				s = int32(i)
 			}
-			if sa[i] == len(sa)-1 {
+			if sa[i] == int32(len(sa))-1 {
 				sa[i], sa[s] = sa[s], sa[i]
 				inv[sa[s]] = s
 				sa[s] = -1 // mark it as an isolated sorted group
@@ -131,31 +133,31 @@ func initGroups(sa []int, data []byte) []int {
 	return inv
 }
 
-type suffixSortable struct {
-	sa  []int
-	inv []int
-	h   int
-	buf []int // common scratch space
+type suffixSortable32 struct {
+	sa  []int32
+	inv []int32
+	h   int32
+	buf []int32 // common scratch space
 }
 
-func (x *suffixSortable) Len() int           { return len(x.sa) }
-func (x *suffixSortable) Less(i, j int) bool { return x.inv[x.sa[i]+x.h] < x.inv[x.sa[j]+x.h] }
-func (x *suffixSortable) Swap(i, j int)      { x.sa[i], x.sa[j] = x.sa[j], x.sa[i] }
+func (x *suffixSortable32) Len() int           { return len(x.sa) }
+func (x *suffixSortable32) Less(i, j int) bool { return x.inv[x.sa[i]+x.h] < x.inv[x.sa[j]+x.h] }
+func (x *suffixSortable32) Swap(i, j int)      { x.sa[i], x.sa[j] = x.sa[j], x.sa[i] }
 
-func (x *suffixSortable) updateGroups(offset int) {
+func (x *suffixSortable32) updateGroups(offset int32) {
 	bounds := x.buf[0:0]
 	group := x.inv[x.sa[0]+x.h]
 	for i := 1; i < len(x.sa); i++ {
 		if g := x.inv[x.sa[i]+x.h]; g > group {
-			bounds = append(bounds, i)
+			bounds = append(bounds, int32(i))
 			group = g
 		}
 	}
-	bounds = append(bounds, len(x.sa))
+	bounds = append(bounds, int32(len(x.sa)))
 	x.buf = bounds
 
 	// update the group numberings after all new groups are determined
-	prev := 0
+	prev := int32(0)
 	for _, b := range bounds {
 		for i := prev; i < b; i++ {
 			x.inv[x.sa[i]] = offset + b - 1
diff --git a/src/index/suffixarray/qsufsort64.go b/src/index/suffixarray/qsufsort64.go
new file mode 100644
index 0000000000..907d6e3726
--- /dev/null
+++ b/src/index/suffixarray/qsufsort64.go
@@ -0,0 +1,173 @@
+// 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.
+
+// Code generated by gen64.go; DO NOT EDIT.
+//go:generate go run gen64.go
+
+// This algorithm is based on "Faster Suffix Sorting"
+//   by N. Jesper Larsson and Kunihiko Sadakane
+// paper: http://www.larsson.dogma.net/ssrev-tr.pdf
+// code:  http://www.larsson.dogma.net/qsufsort.c
+
+// This algorithm computes the suffix array sa by computing its inverse.
+// Consecutive groups of suffixes in sa are labeled as sorted groups or
+// unsorted groups. For a given pass of the sorter, all suffixes are ordered
+// up to their first h characters, and sa is h-ordered. Suffixes in their
+// final positions and unambiguously sorted in h-order are in a sorted group.
+// Consecutive groups of suffixes with identical first h characters are an
+// unsorted group. In each pass of the algorithm, unsorted groups are sorted
+// according to the group number of their following suffix.
+
+// In the implementation, if sa[i] is negative, it indicates that i is
+// the first element of a sorted group of length -sa[i], and can be skipped.
+// An unsorted group sa[i:k] is given the group number of the index of its
+// last element, k-1. The group numbers are stored in the inverse slice (inv),
+// and when all groups are sorted, this slice is the inverse suffix array.
+
+package suffixarray
+
+import (
+	"sort"
+)
+
+func qsufsort64(data []byte) []int64 {
+	// initial sorting by first byte of suffix
+	sa := sortedByFirstByte64(data)
+	if len(sa) < 2 {
+		return sa
+	}
+	// initialize the group lookup table
+	// this becomes the inverse of the suffix array when all groups are sorted
+	inv := initGroups64(sa, data)
+
+	// the index starts 1-ordered
+	sufSortable := &suffixSortable64{sa: sa, inv: inv, h: 1}
+
+	for sa[0] > -int64(len(sa)) { // until all suffixes are one big sorted group
+		// The suffixes are h-ordered, make them 2*h-ordered
+		pi := int64(0) // pi is first position of first group
+		sl := int64(0) // sl is negated length of sorted groups
+		for pi < int64(len(sa)) {
+			if s := sa[pi]; s < 0 { // if pi starts sorted group
+				pi -= s // skip over sorted group
+				sl += s // add negated length to sl
+			} else { // if pi starts unsorted group
+				if sl != 0 {
+					sa[pi+sl] = sl // combine sorted groups before pi
+					sl = 0
+				}
+				pk := inv[s] + 1 // pk-1 is last position of unsorted group
+				sufSortable.sa = sa[pi:pk]
+				sort.Sort(sufSortable)
+				sufSortable.updateGroups(pi)
+				pi = pk // next group
+			}
+		}
+		if sl != 0 { // if the array ends with a sorted group
+			sa[pi+sl] = sl // combine sorted groups at end of sa
+		}
+
+		sufSortable.h *= 2 // double sorted depth
+	}
+
+	for i := range sa { // reconstruct suffix array from inverse
+		sa[inv[i]] = int64(i)
+	}
+	return sa
+}
+
+func sortedByFirstByte64(data []byte) []int64 {
+	// total byte counts
+	var count [256]int
+	for _, b := range data {
+		count[b]++
+	}
+	// make count[b] equal index of first occurrence of b in sorted array
+	sum := 0
+	for b := range count {
+		count[b], sum = sum, count[b]+sum
+	}
+	// iterate through bytes, placing index into the correct spot in sa
+	sa := make([]int64, len(data))
+	for i, b := range data {
+		sa[count[b]] = int64(i)
+		count[b]++
+	}
+	return sa
+}
+
+func initGroups64(sa []int64, data []byte) []int64 {
+	// label contiguous same-letter groups with the same group number
+	inv := make([]int64, len(data))
+	prevGroup := int64(len(sa)) - 1
+	groupByte := data[sa[prevGroup]]
+	for i := int64(len(sa)) - 1; i >= 0; i-- {
+		if b := data[sa[i]]; b < groupByte {
+			if prevGroup == i+1 {
+				sa[i+1] = -1
+			}
+			groupByte = b
+			prevGroup = i
+		}
+		inv[sa[i]] = prevGroup
+		if prevGroup == 0 {
+			sa[0] = -1
+		}
+	}
+	// Separate out the final suffix to the start of its group.
+	// This is necessary to ensure the suffix "a" is before "aba"
+	// when using a potentially unstable sort.
+	lastByte := data[len(data)-1]
+	s := int64(-1)
+	for i := range sa {
+		if sa[i] >= 0 {
+			if data[sa[i]] == lastByte && s == -1 {
+				s = int64(i)
+			}
+			if sa[i] == int64(len(sa))-1 {
+				sa[i], sa[s] = sa[s], sa[i]
+				inv[sa[s]] = s
+				sa[s] = -1 // mark it as an isolated sorted group
+				break
+			}
+		}
+	}
+	return inv
+}
+
+type suffixSortable64 struct {
+	sa  []int64
+	inv []int64
+	h   int64
+	buf []int64 // common scratch space
+}
+
+func (x *suffixSortable64) Len() int           { return len(x.sa) }
+func (x *suffixSortable64) Less(i, j int) bool { return x.inv[x.sa[i]+x.h] < x.inv[x.sa[j]+x.h] }
+func (x *suffixSortable64) Swap(i, j int)      { x.sa[i], x.sa[j] = x.sa[j], x.sa[i] }
+
+func (x *suffixSortable64) updateGroups(offset int64) {
+	bounds := x.buf[0:0]
+	group := x.inv[x.sa[0]+x.h]
+	for i := 1; i < len(x.sa); i++ {
+		if g := x.inv[x.sa[i]+x.h]; g > group {
+			bounds = append(bounds, int64(i))
+			group = g
+		}
+	}
+	bounds = append(bounds, int64(len(x.sa)))
+	x.buf = bounds
+
+	// update the group numberings after all new groups are determined
+	prev := int64(0)
+	for _, b := range bounds {
+		for i := prev; i < b; i++ {
+			x.inv[x.sa[i]] = offset + b - 1
+		}
+		if b-prev == 1 {
+			x.sa[prev] = -1
+		}
+		prev = b
+	}
+}
diff --git a/src/index/suffixarray/suffixarray.go b/src/index/suffixarray/suffixarray.go
index 0961ac4fb2..339643db4d 100644
--- a/src/index/suffixarray/suffixarray.go
+++ b/src/index/suffixarray/suffixarray.go
@@ -19,21 +19,68 @@ package suffixarray
 import (
 	"bytes"
 	"encoding/binary"
+	"errors"
 	"io"
+	"math"
 	"regexp"
 	"sort"
 )
 
+// Can change for testing
+var maxData32 int = realMaxData32
+
+const realMaxData32 = math.MaxInt32
+
 // Index implements a suffix array for fast substring search.
 type Index struct {
 	data []byte
-	sa   []int // suffix array for data; len(sa) == len(data)
+	sa   ints // suffix array for data; sa.len() == len(data)
+}
+
+// An ints is either an []int32 or an []int64.
+// That is, one of them is empty, and one is the real data.
+// The int64 form is used when len(data) > maxData32
+type ints struct {
+	int32 []int32
+	int64 []int64
+}
+
+func (a *ints) len() int {
+	return len(a.int32) + len(a.int64)
+}
+
+func (a *ints) get(i int) int64 {
+	if a.int32 != nil {
+		return int64(a.int32[i])
+	}
+	return a.int64[i]
+}
+
+func (a *ints) set(i int, v int64) {
+	if a.int32 != nil {
+		a.int32[i] = int32(v)
+	} else {
+		a.int64[i] = v
+	}
+}
+
+func (a *ints) slice(i, j int) ints {
+	if a.int32 != nil {
+		return ints{a.int32[i:j], nil}
+	}
+	return ints{nil, a.int64[i:j]}
 }
 
 // New creates a new Index for data.
 // Index creation time is O(N*log(N)) for N = len(data).
 func New(data []byte) *Index {
-	return &Index{data, qsufsort(data)}
+	ix := &Index{data: data}
+	if len(data) <= maxData32 {
+		ix.sa.int32 = qsufsort32(data)
+	} else {
+		ix.sa.int64 = qsufsort64(data)
+	}
+	return ix
 }
 
 // writeInt writes an int x to w using buf to buffer the write.
@@ -44,19 +91,20 @@ func writeInt(w io.Writer, buf []byte, x int) error {
 }
 
 // readInt reads an int x from r using buf to buffer the read and returns x.
-func readInt(r io.Reader, buf []byte) (int, error) {
+func readInt(r io.Reader, buf []byte) (int64, error) {
 	_, err := io.ReadFull(r, buf[0:binary.MaxVarintLen64]) // ok to continue with error
 	x, _ := binary.Varint(buf)
-	return int(x), err
+	return x, err
 }
 
 // writeSlice writes data[:n] to w and returns n.
 // It uses buf to buffer the write.
-func writeSlice(w io.Writer, buf []byte, data []int) (n int, err error) {
+func writeSlice(w io.Writer, buf []byte, data ints) (n int, err error) {
 	// encode as many elements as fit into buf
 	p := binary.MaxVarintLen64
-	for ; n < len(data) && p+binary.MaxVarintLen64 <= len(buf); n++ {
-		p += binary.PutUvarint(buf[p:], uint64(data[n]))
+	m := data.len()
+	for ; n < m && p+binary.MaxVarintLen64 <= len(buf); n++ {
+		p += binary.PutUvarint(buf[p:], uint64(data.get(n)))
 	}
 
 	// update buffer size
@@ -67,15 +115,22 @@ func writeSlice(w io.Writer, buf []byte, data []int) (n int, err error) {
 	return
 }
 
+var errTooBig = errors.New("suffixarray: data too large")
+
 // readSlice reads data[:n] from r and returns n.
 // It uses buf to buffer the read.
-func readSlice(r io.Reader, buf []byte, data []int) (n int, err error) {
+func readSlice(r io.Reader, buf []byte, data ints) (n int, err error) {
 	// read buffer size
-	var size int
-	size, err = readInt(r, buf)
+	var size64 int64
+	size64, err = readInt(r, buf)
 	if err != nil {
 		return
 	}
+	if int64(int(size64)) != size64 || int(size64) < 0 {
+		// We never write chunks this big anyway.
+		return 0, errTooBig
+	}
+	size := int(size64)
 
 	// read buffer w/o the size
 	if _, err = io.ReadFull(r, buf[binary.MaxVarintLen64:size]); err != nil {
@@ -85,7 +140,7 @@ func readSlice(r io.Reader, buf []byte, data []int) (n int, err error) {
 	// decode as many elements as present in buf
 	for p := binary.MaxVarintLen64; p < size; n++ {
 		x, w := binary.Uvarint(buf[p:])
-		data[n] = int(x)
+		data.set(n, int64(x))
 		p += w
 	}
 
@@ -100,21 +155,31 @@ func (x *Index) Read(r io.Reader) error {
 	buf := make([]byte, bufSize)
 
 	// read length
-	n, err := readInt(r, buf)
+	n64, err := readInt(r, buf)
 	if err != nil {
 		return err
 	}
+	if int64(int(n64)) != n64 || int(n64) < 0 {
+		return errTooBig
+	}
+	n := int(n64)
 
 	// allocate space
-	if 2*n < cap(x.data) || cap(x.data) < n {
+	if 2*n < cap(x.data) || cap(x.data) < n || x.sa.int32 != nil && n > maxData32 || x.sa.int64 != nil && n <= maxData32 {
 		// new data is significantly smaller or larger than
 		// existing buffers - allocate new ones
 		x.data = make([]byte, n)
-		x.sa = make([]int, n)
+		x.sa.int32 = nil
+		x.sa.int64 = nil
+		if n <= maxData32 {
+			x.sa.int32 = make([]int32, n)
+		} else {
+			x.sa.int64 = make([]int64, n)
+		}
 	} else {
 		// re-use existing buffers
 		x.data = x.data[0:n]
-		x.sa = x.sa[0:n]
+		x.sa = x.sa.slice(0, n)
 	}
 
 	// read data
@@ -123,12 +188,13 @@ func (x *Index) Read(r io.Reader) error {
 	}
 
 	// read index
-	for sa := x.sa; len(sa) > 0; {
+	sa := x.sa
+	for sa.len() > 0 {
 		n, err := readSlice(r, buf, sa)
 		if err != nil {
 			return err
 		}
-		sa = sa[n:]
+		sa = sa.slice(n, sa.len())
 	}
 	return nil
 }
@@ -149,12 +215,13 @@ func (x *Index) Write(w io.Writer) error {
 	}
 
 	// write index
-	for sa := x.sa; len(sa) > 0; {
+	sa := x.sa
+	for sa.len() > 0 {
 		n, err := writeSlice(w, buf, sa)
 		if err != nil {
 			return err
 		}
-		sa = sa[n:]
+		sa = sa.slice(n, sa.len())
 	}
 	return nil
 }
@@ -167,18 +234,18 @@ func (x *Index) Bytes() []byte {
 }
 
 func (x *Index) at(i int) []byte {
-	return x.data[x.sa[i]:]
+	return x.data[x.sa.get(i):]
 }
 
 // lookupAll returns a slice into the matching region of the index.
 // The runtime is O(log(N)*len(s)).
-func (x *Index) lookupAll(s []byte) []int {
+func (x *Index) lookupAll(s []byte) ints {
 	// find matching suffix index range [i:j]
 	// find the first index where s would be the prefix
-	i := sort.Search(len(x.sa), func(i int) bool { return bytes.Compare(x.at(i), s) >= 0 })
+	i := sort.Search(x.sa.len(), func(i int) bool { return bytes.Compare(x.at(i), s) >= 0 })
 	// starting at i, find the first index at which s is not a prefix
-	j := i + sort.Search(len(x.sa)-i, func(j int) bool { return !bytes.HasPrefix(x.at(j+i), s) })
-	return x.sa[i:j]
+	j := i + sort.Search(x.sa.len()-i, func(j int) bool { return !bytes.HasPrefix(x.at(j+i), s) })
+	return x.sa.slice(i, j)
 }
 
 // Lookup returns an unsorted list of at most n indices where the byte string s
@@ -190,13 +257,22 @@ func (x *Index) lookupAll(s []byte) []int {
 func (x *Index) Lookup(s []byte, n int) (result []int) {
 	if len(s) > 0 && n != 0 {
 		matches := x.lookupAll(s)
-		if n < 0 || len(matches) < n {
-			n = len(matches)
+		count := matches.len()
+		if n < 0 || count < n {
+			n = count
 		}
-		// 0 <= n <= len(matches)
+		// 0 <= n <= count
 		if n > 0 {
 			result = make([]int, n)
-			copy(result, matches)
+			if matches.int32 != nil {
+				for i := range result {
+					result[i] = int(matches.int32[i])
+				}
+			} else {
+				for i := range result {
+					result[i] = int(matches.int64[i])
+				}
+			}
 		}
 	}
 	return
diff --git a/src/index/suffixarray/suffixarray_test.go b/src/index/suffixarray/suffixarray_test.go
index 644f00c757..3cb8450105 100644
--- a/src/index/suffixarray/suffixarray_test.go
+++ b/src/index/suffixarray/suffixarray_test.go
@@ -6,7 +6,11 @@ package suffixarray
 
 import (
 	"bytes"
+	"fmt"
+	"io/ioutil"
 	"math/rand"
+	"os"
+	"path/filepath"
 	"regexp"
 	"sort"
 	"strings"
@@ -207,10 +211,19 @@ func testLookups(t *testing.T, tc *testCase, x *Index, n int) {
 // index is used to hide the sort.Interface
 type index Index
 
-func (x *index) Len() int           { return len(x.sa) }
+func (x *index) Len() int           { return x.sa.len() }
 func (x *index) Less(i, j int) bool { return bytes.Compare(x.at(i), x.at(j)) < 0 }
-func (x *index) Swap(i, j int)      { x.sa[i], x.sa[j] = x.sa[j], x.sa[i] }
-func (a *index) at(i int) []byte    { return a.data[a.sa[i]:] }
+func (x *index) Swap(i, j int) {
+	if x.sa.int32 != nil {
+		x.sa.int32[i], x.sa.int32[j] = x.sa.int32[j], x.sa.int32[i]
+	} else {
+		x.sa.int64[i], x.sa.int64[j] = x.sa.int64[j], x.sa.int64[i]
+	}
+}
+
+func (x *index) at(i int) []byte {
+	return x.data[x.sa.get(i):]
+}
 
 func testConstruction(t *testing.T, tc *testCase, x *Index) {
 	if !sort.IsSorted((*index)(x)) {
@@ -222,8 +235,12 @@ func equal(x, y *Index) bool {
 	if !bytes.Equal(x.data, y.data) {
 		return false
 	}
-	for i, j := range x.sa {
-		if j != y.sa[i] {
+	if x.sa.len() != y.sa.len() {
+		return false
+	}
+	n := x.sa.len()
+	for i := 0; i < n; i++ {
+		if x.sa.get(i) != y.sa.get(i) {
 			return false
 		}
 	}
@@ -238,16 +255,41 @@ func testSaveRestore(t *testing.T, tc *testCase, x *Index) int {
 	}
 	size := buf.Len()
 	var y Index
-	if err := y.Read(&buf); err != nil {
+	if err := y.Read(bytes.NewReader(buf.Bytes())); err != nil {
+		t.Errorf("failed reading index %s (%s)", tc.name, err)
+	}
+	if !equal(x, &y) {
+		t.Errorf("restored index doesn't match saved index %s", tc.name)
+	}
+
+	old := maxData32
+	defer func() {
+		maxData32 = old
+	}()
+	// Reread as forced 32.
+	y = Index{}
+	maxData32 = realMaxData32
+	if err := y.Read(bytes.NewReader(buf.Bytes())); err != nil {
+		t.Errorf("failed reading index %s (%s)", tc.name, err)
+	}
+	if !equal(x, &y) {
+		t.Errorf("restored index doesn't match saved index %s", tc.name)
+	}
+
+	// Reread as forced 64.
+	y = Index{}
+	maxData32 = -1
+	if err := y.Read(bytes.NewReader(buf.Bytes())); err != nil {
 		t.Errorf("failed reading index %s (%s)", tc.name, err)
 	}
 	if !equal(x, &y) {
 		t.Errorf("restored index doesn't match saved index %s", tc.name)
 	}
+
 	return size
 }
 
-func TestIndex(t *testing.T) {
+func testIndex(t *testing.T) {
 	for _, tc := range testCases {
 		x := New([]byte(tc.source))
 		testConstruction(t, &tc, x)
@@ -260,45 +302,162 @@ func TestIndex(t *testing.T) {
 	}
 }
 
+func TestIndex32(t *testing.T) {
+	testIndex(t)
+}
+
+func TestIndex64(t *testing.T) {
+	maxData32 = -1
+	defer func() {
+		maxData32 = realMaxData32
+	}()
+	testIndex(t)
+}
+
+var (
+	benchdata = make([]byte, 1e6)
+	benchrand = make([]byte, 1e6)
+)
+
 // Of all possible inputs, the random bytes have the least amount of substring
 // repetition, and the repeated bytes have the most. For most algorithms,
 // the running time of every input will be between these two.
 func benchmarkNew(b *testing.B, random bool) {
+	b.ReportAllocs()
 	b.StopTimer()
-	data := make([]byte, 1e6)
+	data := benchdata
 	if random {
-		for i := range data {
-			data[i] = byte(rand.Intn(256))
+		data = benchrand
+		if data[0] == 0 {
+			for i := range data {
+				data[i] = byte(rand.Intn(256))
+			}
 		}
 	}
 	b.StartTimer()
+	b.SetBytes(int64(len(data)))
 	for i := 0; i < b.N; i++ {
 		New(data)
 	}
 }
 
-func BenchmarkNewIndexRandom(b *testing.B) {
-	benchmarkNew(b, true)
+func makeText(name string) ([]byte, error) {
+	var data []byte
+	switch name {
+	case "opticks":
+		var err error
+		data, err = ioutil.ReadFile("../../testdata/Isaac.Newton-Opticks.txt")
+		if err != nil {
+			return nil, err
+		}
+	case "go":
+		err := filepath.Walk("../..", func(path string, info os.FileInfo, err error) error {
+			if err == nil && strings.HasSuffix(path, ".go") && !info.IsDir() {
+				file, err := ioutil.ReadFile(path)
+				if err != nil {
+					return err
+				}
+				data = append(data, file...)
+			}
+			return nil
+		})
+		if err != nil {
+			return nil, err
+		}
+	case "zero":
+		data = make([]byte, 50e6)
+	case "rand":
+		data = make([]byte, 50e6)
+		for i := range data {
+			data[i] = byte(rand.Intn(256))
+		}
+	}
+	return data, nil
 }
-func BenchmarkNewIndexRepeat(b *testing.B) {
-	benchmarkNew(b, false)
+
+func setBits(bits int) (cleanup func()) {
+	if bits == 32 {
+		maxData32 = realMaxData32
+	} else {
+		maxData32 = -1 // force use of 64-bit code
+	}
+	return func() {
+		maxData32 = realMaxData32
+	}
+}
+
+func BenchmarkNew(b *testing.B) {
+	for _, text := range []string{"opticks", "go", "zero", "rand"} {
+		b.Run("text="+text, func(b *testing.B) {
+			data, err := makeText(text)
+			if err != nil {
+				b.Fatal(err)
+			}
+			if testing.Short() && len(data) > 5e6 {
+				data = data[:5e6]
+			}
+			for _, size := range []int{100e3, 500e3, 1e6, 5e6, 10e6, 50e6} {
+				if len(data) < size {
+					continue
+				}
+				data := data[:size]
+				name := fmt.Sprintf("%dK", size/1e3)
+				if size >= 1e6 {
+					name = fmt.Sprintf("%dM", size/1e6)
+				}
+				b.Run("size="+name, func(b *testing.B) {
+					for _, bits := range []int{32, 64} {
+						if ^uint(0) == 0xffffffff && bits == 64 {
+							continue
+						}
+						b.Run(fmt.Sprintf("bits=%d", bits), func(b *testing.B) {
+							cleanup := setBits(bits)
+							defer cleanup()
+
+							b.SetBytes(int64(len(data)))
+							b.ReportAllocs()
+							for i := 0; i < b.N; i++ {
+								New(data)
+							}
+						})
+					}
+				})
+			}
+		})
+	}
 }
 
 func BenchmarkSaveRestore(b *testing.B) {
-	b.StopTimer()
 	r := rand.New(rand.NewSource(0x5a77a1)) // guarantee always same sequence
 	data := make([]byte, 1<<20)             // 1MB of data to index
 	for i := range data {
 		data[i] = byte(r.Intn(256))
 	}
-	x := New(data)
-	size := testSaveRestore(nil, nil, x)       // verify correctness
-	buf := bytes.NewBuffer(make([]byte, size)) // avoid growing
-	b.SetBytes(int64(size))
-	b.StartTimer()
-	for i := 0; i < b.N; i++ {
-		x.Write(buf)
-		var y Index
-		y.Read(buf)
+	for _, bits := range []int{32, 64} {
+		if ^uint(0) == 0xffffffff && bits == 64 {
+			continue
+		}
+		b.Run(fmt.Sprintf("bits=%d", bits), func(b *testing.B) {
+			cleanup := setBits(bits)
+			defer cleanup()
+
+			b.StopTimer()
+			x := New(data)
+			size := testSaveRestore(nil, nil, x)       // verify correctness
+			buf := bytes.NewBuffer(make([]byte, size)) // avoid growing
+			b.SetBytes(int64(size))
+			b.StartTimer()
+			b.ReportAllocs()
+			for i := 0; i < b.N; i++ {
+				buf.Reset()
+				if err := x.Write(buf); err != nil {
+					b.Fatal(err)
+				}
+				var y Index
+				if err := y.Read(buf); err != nil {
+					b.Fatal(err)
+				}
+			}
+		})
 	}
 }