chaincfg: Avoid block 1 subsidy codegen explosion.

chaincfg/v2 modified the Params type to contain the required payouts
created by the miner of the block at height 1.  However, it was
discovered that, due to code generation issues of the Go compiler,
this caused the package's weight (measured by
github.com/jondot/goweight) to explode to 7.7 MB.  This appears to be
due to an enormous amount of function calls, all of which could panic,
when building the large slice literal.

This improves the compiled size of the package by using code
generation techniques to optimize the memory layout and code
transformation of the subsidy values each time a params function is
called.  A single string contains all scripts for subsidy payouts
concatenated together, in hex encoding, and a slice contains the index
in the script data and the required payout amount.  This is iterated
in a loop to create a []TokenPayout each time it is needed.

The new size of the compiled package using Go 1.12.7 on OpenBSD/amd64
is 379 kB, a reduction of 7.32 MB, and about 5% of the original size.

chaincfg/generatesubsidytables.go

@@ -0,0 +1,97 @@
+// Copyright (c) 2019 The Decred developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+//+build ignore
+
+package main
+
+import (
+	"bytes"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"strings"
+
+	"github.com/decred/dcrd/chaincfg/v2"
+)
+
+type payout struct {
+	offset int
+	amount int64
+}
+
+type payouts []payout
+
+func (p payouts) GoString() string {
+	var s strings.Builder
+	s.WriteString("[]blockOnePayout{\n")
+	for i := range p {
+		s.WriteString("\t")
+		s.WriteString(fmt.Sprintf("{offset: %#v, amount: %#v}", p[i].offset, p[i].amount))
+		s.WriteString(",\n")
+	}
+	s.WriteString("}")
+	return s.String()
+}
+
+type printer func(format string, args ...interface{})
+
+func main() {
+	buf := new(bytes.Buffer)
+	p := func(format string, args ...interface{}) {
+		fmt.Fprintf(buf, format, args...)
+	}
+
+	p("// autogenerated by generatesubsidytable.go; do not edit\n\n")
+	p("package chaincfg\n")
+	for _, g := range []struct {
+		name         string
+		tokenPayouts []chaincfg.TokenPayout
+	}{
+		{"MainNetParams", chaincfg.MainNetSubsidyDefinition},
+		{"TestNet3Params", chaincfg.TestNet3SubsidyDefinition},
+		{"SimNetParams", chaincfg.SimNetSubsidyDefinition},
+		{"RegNetParams", chaincfg.RegNetSubsidyDefinition},
+	} {
+		p("\n")
+		defs(p, g.name, g.tokenPayouts)
+	}
+
+	out, err := os.Create("subsidytables.go")
+	if err != nil {
+		log.Fatal(err)
+	}
+	_, err = io.Copy(out, buf)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func defs(p printer, paramsName string, tokenPayouts []chaincfg.TokenPayout) {
+	var scripts strings.Builder
+	var payouts payouts
+	var offset int
+	for _, t := range tokenPayouts {
+		if t.ScriptVersion != 0 {
+			log.Fatalf("this tool only generates code where all scripts are version 0")
+		}
+		_, err := scripts.WriteString(hex.EncodeToString(t.Script))
+		if err != nil {
+			log.Panic(err)
+		}
+		offset += len(t.Script)
+		payouts = append(payouts, payout{
+			offset: offset,
+			amount: t.Amount,
+		})
+	}
+
+	p("const blockOnePayoutScripts_%s = %#v\n\n", paramsName, scripts.String())
+	p("var blockOnePayouts_%s = %#v\n\n", paramsName, payouts)
+	p("func tokenPayouts_%s() []TokenPayout {\n"+
+		"\treturn tokenPayouts(blockOnePayoutScripts_%[1]s, blockOnePayouts_%[1]s)\n"+
+		"}\n", paramsName)
+}

chaincfg/regnetparams.go

@@ -318,10 +318,6 @@ func RegNetParams() *Params {
 		// Organization address is RcQR65gasxuzf7mUeBXeAux6Z37joPuUwUN
 		OrganizationPkScript:        hexDecode("a9146913bcc838bd0087fb3f6b3c868423d5e300078d87"),
 		OrganizationPkScriptVersion: 0,
-		BlockOneLedger: []TokenPayout{
-			mustPayout("76a9147e4765ae88ba9ad5c9e4715c484e90b34d358d5188ac", 100000*1e8),
-			mustPayout("76a91402fb1ac0137666d79165e13cecd403883615270788ac", 100000*1e8),
-			mustPayout("76a91469de627d3231b14228653dd09cba75eeb872754288ac", 100000*1e8),
-		},
+		BlockOneLedger:              tokenPayouts_RegNetParams(),
 	}
 }

chaincfg/simnetparams.go

@@ -203,10 +203,6 @@ func SimNetParams() *Params {
 		// Organization address is ScuQxvveKGfpG1ypt6u27F99Anf7EW3cqhq
 		OrganizationPkScript:        hexDecode("a914cbb08d6ca783b533b2c7d24a51fbca92d937bf9987"),
 		OrganizationPkScriptVersion: 0,
-		BlockOneLedger: []TokenPayout{
-			mustPayout("76a91494ff37a0ee4d48abc45f70474f9b86f9da69a70988ac", 100000*1e8),
-			mustPayout("76a914a6753ebbc08e2553e7dd6d64bdead4bcbff4fcf188ac", 100000*1e8),
-			mustPayout("76a9147aa3211c2ead810bbf5911c275c69cc196202bd888ac", 100000*1e8),
-		},
+		BlockOneLedger:              tokenPayouts_SimNetParams(),
 	}
 }

chaincfg/subsidy.go

@@ -0,0 +1,27 @@
+// Copyright (c) 2019 The Decred developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package chaincfg
+
+//go:generate go run -tags subsidydefs generatesubsidytables.go
+
+type blockOnePayout struct {
+	offset int
+	amount int64
+}
+
+func tokenPayouts(scriptsHex string, payouts []blockOnePayout) []TokenPayout {
+	tokenPayouts := make([]TokenPayout, len(payouts))
+	var offset int
+	scripts := hexDecode(scriptsHex)
+	for i := range payouts {
+		tokenPayouts[i] = TokenPayout{
+			ScriptVersion: 0,
+			Script:        scripts[offset:payouts[i].offset],
+			Amount:        payouts[i].amount,
+		}
+		offset = payouts[i].offset
+	}
+	return tokenPayouts
+}

chaincfg/testnetparams.go

@@ -204,9 +204,6 @@ func TestNet3Params() *Params {
 		// Organization address is TcrypGAcGCRVXrES7hWqVZb5oLJKCZEtoL1.
 		OrganizationPkScript:        hexDecode("a914d585cd7426d25b4ea5faf1e6987aacfeda3db94287"),
 		OrganizationPkScriptVersion: 0,
-		BlockOneLedger: []TokenPayout{
-			mustPayout("76a914bb56576997d9f7abeebac585821b4d9a79d7ea0a88ac", 80000*1e8),
-			mustPayout("76a9147a5c4cca76f2e0b36db4763daacbd6cbb6ee6e7b88ac", 20000*1e8),
-		},
+		BlockOneLedger:              tokenPayouts_TestNet3Params(),
 	}
 }