libs : Remove libs/common/word.go (#2431)

We didn't use this code anywhere in the codebase. As such, we probably
should reduce the surface area we support. In the event that we do
in fact require 256 bit words inside of tendermint, we should adapt
the stdlibs' internal word representations, which also handles SIMD.

Inside of the SDK, a separate solution for big ints / larger words
is employed, which uses big ints. This in turn does utilize the stdlibs
SIMD support.

CHANGELOG_PENDING.md

@@ -11,6 +11,7 @@ BREAKING CHANGES:
 
 * Go API
   * \#2310 Mempool.ReapMaxBytes -> Mempool.ReapMaxBytesMaxGas
+  * \#2431 Remove Word256 code in libs/common, due to lack of use
 * Blockchain Protocol
 
 * P2P Protocol

libs/common/word.go

@@ -1,90 +0,0 @@
-package common
-
-import (
-	"bytes"
-	"sort"
-)
-
-var (
-	Zero256 = Word256{0}
-	One256  = Word256{1}
-)
-
-type Word256 [32]byte
-
-func (w Word256) String() string        { return string(w[:]) }
-func (w Word256) TrimmedString() string { return TrimmedString(w.Bytes()) }
-func (w Word256) Copy() Word256         { return w }
-func (w Word256) Bytes() []byte         { return w[:] } // copied.
-func (w Word256) Prefix(n int) []byte   { return w[:n] }
-func (w Word256) Postfix(n int) []byte  { return w[32-n:] }
-func (w Word256) IsZero() bool {
-	accum := byte(0)
-	for _, byt := range w {
-		accum |= byt
-	}
-	return accum == 0
-}
-func (w Word256) Compare(other Word256) int {
-	return bytes.Compare(w[:], other[:])
-}
-
-func Uint64ToWord256(i uint64) Word256 {
-	buf := [8]byte{}
-	PutUint64BE(buf[:], i)
-	return LeftPadWord256(buf[:])
-}
-
-func Int64ToWord256(i int64) Word256 {
-	buf := [8]byte{}
-	PutInt64BE(buf[:], i)
-	return LeftPadWord256(buf[:])
-}
-
-func RightPadWord256(bz []byte) (word Word256) {
-	copy(word[:], bz)
-	return
-}
-
-func LeftPadWord256(bz []byte) (word Word256) {
-	copy(word[32-len(bz):], bz)
-	return
-}
-
-func Uint64FromWord256(word Word256) uint64 {
-	buf := word.Postfix(8)
-	return GetUint64BE(buf)
-}
-
-func Int64FromWord256(word Word256) int64 {
-	buf := word.Postfix(8)
-	return GetInt64BE(buf)
-}
-
-//-------------------------------------
-
-type Tuple256 struct {
-	First  Word256
-	Second Word256
-}
-
-func (tuple Tuple256) Compare(other Tuple256) int {
-	firstCompare := tuple.First.Compare(other.First)
-	if firstCompare == 0 {
-		return tuple.Second.Compare(other.Second)
-	}
-	return firstCompare
-}
-
-func Tuple256Split(t Tuple256) (Word256, Word256) {
-	return t.First, t.Second
-}
-
-type Tuple256Slice []Tuple256
-
-func (p Tuple256Slice) Len() int { return len(p) }
-func (p Tuple256Slice) Less(i, j int) bool {
-	return p[i].Compare(p[j]) < 0
-}
-func (p Tuple256Slice) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
-func (p Tuple256Slice) Sort()         { sort.Sort(p) }