From e780e41e0222517caa9c69030b5955ab2b458a49 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Olivier=20Mengu=C3=A9?= <dolmen@cpan.org>
Date: Sat, 2 Feb 2019 04:05:01 +0100
Subject: Faster TitleToNumber (#343)

* TestTitleToNumber: more test cases

* TitleToNumber: drop use of math.Pow()

Compute using pure integers

* TitleToNumber: simplify

Remove unecessary casts to int
---
 lib.go | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

(limited to 'lib.go')

diff --git a/lib.go b/lib.go
index 99c513e..30a20e0 100644
--- a/lib.go
+++ b/lib.go
@@ -14,7 +14,6 @@ import (
 	"bytes"
 	"io"
 	"log"
-	"math"
 	"strconv"
 	"strings"
 	"unicode"
@@ -91,15 +90,15 @@ func ToAlphaString(value int) string {
 //    excelize.TitleToNumber("ak")
 //
 func TitleToNumber(s string) int {
-	weight := 0.0
+	weight := 1
 	sum := 0
 	for i := len(s) - 1; i >= 0; i-- {
-		ch := int(s[i])
-		if int(s[i]) >= int('a') && int(s[i]) <= int('z') {
-			ch = int(s[i]) - 32
+		ch := s[i]
+		if ch >= 'a' && ch <= 'z' {
+			ch -= 32
 		}
-		sum = sum + (ch-int('A')+1)*int(math.Pow(26, weight))
-		weight++
+		sum += int(ch-'A'+1) * weight
+		weight *= 26
 	}
 	return sum - 1
 }
-- 
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