cmd/addchain: templated output generation (#127)

Provides support for templated output based on addition chain programs.
The new `addchain gen` subcommand allows for templated output, including some
built-in templates.

The new feature has full documentation, auto-generated as usual to keep in
sync:

* Full working example of fp25519 inversion
* Template input data and functions
* Example output for all builtin templates

Fixes #94

.golangci.yml

@@ -15,6 +15,7 @@ linters:
     - maligned
     - nlreturn
     - paralleltest
+    - prealloc
     - predeclared
     - revive
     - testpackage

README.md

@@ -21,6 +21,7 @@ generators.
 * Generic optimization methods eliminate redundant operations
 * Simple domain-specific language for addition chain computations
 * Command-line interface or library
+* Code generation and templated output support
 
 ## Table of Contents
 
@@ -106,8 +107,8 @@ delta from the library result.
 | [secp256k1 (Bitcoin) Scalar Inversion](doc/results.md#secp256k1-bitcoin-scalar-inversion) | 293 | 290 | +3 |
 
 
-See [full results listing](doc/results.md) for more detail and results for
-less common exponents.
+See [full results listing](doc/results.md) for more detail and
+results for less common exponents.
 
 These results demonstrate that `addchain` is competitive with hand-optimized
 chains, often with equivalent or better performance. Even when `addchain` is
@@ -162,6 +163,8 @@ x250      = x240 << 10 + x10
 return      (x250 << 2 + 1) << 3 + _11
 ```
 
+Next, you can [generate code from this addition chain](doc/gen.md).
+
 ### Library
 
 Install:

acc/printer/printer.go

@@ -11,6 +11,15 @@ import (
 	"github.com/mmcloughlin/addchain/internal/print"
 )
 
+// String prints the AST and returns resulting string.
+func String(n interface{}) (string, error) {
+	b, err := Bytes(n)
+	if err != nil {
+		return "", err
+	}
+	return string(b), nil
+}
+
 // Bytes prints the AST and returns resulting bytes.
 func Bytes(n interface{}) ([]byte, error) {
 	var buf bytes.Buffer

cmd/addchain/gen.go

@@ -0,0 +1,118 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"strings"
+
+	"github.com/google/subcommands"
+
+	"github.com/mmcloughlin/addchain/acc/parse"
+	"github.com/mmcloughlin/addchain/acc/pass"
+	"github.com/mmcloughlin/addchain/internal/cli"
+	"github.com/mmcloughlin/addchain/internal/gen"
+)
+
+// generate subcommand.
+type generate struct {
+	cli.Command
+
+	typ    string
+	tmpl   string
+	output string
+}
+
+func (*generate) Name() string     { return "gen" }
+func (*generate) Synopsis() string { return "generate output from an addition chain program" }
+func (*generate) Usage() string {
+	return `Usage: gen [-type <name>] [-tmpl <file>] [-out <file>] [<filename>]
+
+Generate output from an addition chain program.
+
+`
+}
+
+func (cmd *generate) SetFlags(f *flag.FlagSet) {
+	defaulttype := "listing"
+	if !gen.IsBuiltinTemplate(defaulttype) {
+		panic("bad default template")
+	}
+	f.StringVar(&cmd.typ, "type", defaulttype, fmt.Sprintf("`name` of a builtin template (%s)", strings.Join(gen.BuiltinTemplateNames(), ",")))
+	f.StringVar(&cmd.tmpl, "tmpl", "", "template `file` (overrides type)")
+	f.StringVar(&cmd.output, "out", "", "output `file` (default stdout)")
+}
+
+func (cmd *generate) Execute(_ context.Context, f *flag.FlagSet, _ ...interface{}) (status subcommands.ExitStatus) {
+	// Read input.
+	input, r, err := cli.OpenInput(f.Arg(0))
+	if err != nil {
+		return cmd.Error(err)
+	}
+	defer cmd.CheckClose(&status, r)
+
+	// Parse to a syntax tree.
+	s, err := parse.Reader(input, r)
+	if err != nil {
+		return cmd.Error(err)
+	}
+
+	// Prepare template data.
+	cfg := gen.Config{
+		Allocator: pass.Allocator{
+			Input:  "x",
+			Output: "z",
+			Format: "t%d",
+		},
+	}
+
+	data, err := gen.PrepareData(cfg, s)
+	if err != nil {
+		return cmd.Error(err)
+	}
+
+	// Load template.
+	tmpl, err := cmd.LoadTemplate()
+	if err != nil {
+		return cmd.Error(err)
+	}
+
+	// Open output.
+	_, w, err := cli.OpenOutput(cmd.output)
+	if err != nil {
+		return cmd.Error(err)
+	}
+	defer cmd.CheckClose(&status, w)
+
+	// Generate.
+	if err := gen.Generate(w, tmpl, data); err != nil {
+		return cmd.Error(err)
+	}
+
+	return subcommands.ExitSuccess
+}
+
+func (cmd *generate) LoadTemplate() (string, error) {
+	// Explicit filename has precedence.
+	if cmd.tmpl != "" {
+		b, err := ioutil.ReadFile(cmd.tmpl)
+		if err != nil {
+			return "", err
+		}
+		return string(b), nil
+	}
+
+	// Lookup type name in builtin templates.
+	if cmd.typ == "" {
+		return "", errors.New("no builtin template specified")
+	}
+
+	s, err := gen.BuiltinTemplate(cmd.typ)
+	if err != nil {
+		return "", err
+	}
+
+	return s, nil
+}

cmd/addchain/main.go

@@ -18,6 +18,7 @@ func main() {
 	subcommands.Register(&search{Command: base}, "")
 	subcommands.Register(&eval{Command: base}, "")
 	subcommands.Register(&format{Command: base}, "")
+	subcommands.Register(&generate{Command: base}, "")
 
 	if meta.Meta.BuildVersion != "" {
 		subcommands.Register(&version{version: meta.Meta.BuildVersion, Command: base}, "")