From b836e56a4d8b64a9078157b15873a62e42f786dd Mon Sep 17 00:00:00 2001
From: Igor Mikushkin <igor.mikushkin@gmail.com>
Date: Wed, 29 Aug 2018 02:59:01 +0400
Subject: [PATCH] Using integer operations rather than float in rescale

---
 decimal.go | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/decimal.go b/decimal.go
index 134ece2..7df48f3 100644
--- a/decimal.go
+++ b/decimal.go
@@ -361,11 +361,11 @@ func NewFromFloatWithExponent(value float64, exp int32) Decimal {
 //
 func (d Decimal) rescale(exp int32) Decimal {
 	d.ensureInitialized()
-	// NOTE(vadim): must convert exps to float64 before - to prevent overflow
-	diff := math.Abs(float64(exp) - float64(d.exp))
+	// NOTE(vadim): must convert exps to int64 before - to prevent overflow
+	diff := abs64(int64(exp) - int64(d.exp))
 	value := new(big.Int).Set(d.value)
 
-	expScale := new(big.Int).Exp(tenInt, big.NewInt(int64(diff)), nil)
+	expScale := new(big.Int).Exp(tenInt, big.NewInt(diff), nil)
 	if exp > d.exp {
 		value = value.Quo(value, expScale)
 	} else if exp < d.exp {
@@ -378,6 +378,11 @@ func (d Decimal) rescale(exp int32) Decimal {
 	}
 }
 
+func abs64(n int64) int64 {
+	y := n >> 63
+	return (n ^ y) - y
+}
+
 // Abs returns the absolute value of the decimal.
 func (d Decimal) Abs() Decimal {
 	d.ensureInitialized()