From aae33eb0d12ea3d65976db6c029798b5a69352ca Mon Sep 17 00:00:00 2001
From: c9s <yoanlin93@gmail.com>
Date: Thu, 31 Oct 2024 15:16:26 +0800
Subject: [PATCH] fixedpoint: implement different mul mode

---
 pkg/fixedpoint/convert.go | 67 +++++++++++++++++++++++++++++++++++++--
 1 file changed, 65 insertions(+), 2 deletions(-)

diff --git a/pkg/fixedpoint/convert.go b/pkg/fixedpoint/convert.go
index d000603a8..f61c657fa 100644
--- a/pkg/fixedpoint/convert.go
+++ b/pkg/fixedpoint/convert.go
@@ -8,6 +8,8 @@ import (
 	"errors"
 	"fmt"
 	"math"
+	"math/big"
+	"os"
 	"strconv"
 	"strings"
 	"sync/atomic"
@@ -227,11 +229,11 @@ func (v Value) IsZero() bool {
 }
 
 func Mul(x, y Value) Value {
-	return NewFromFloat(x.Float64() * y.Float64())
+	return mulOp(x, y)
 }
 
 func (v Value) Mul(v2 Value) Value {
-	return NewFromFloat(v.Float64() * v2.Float64())
+	return mulOp(v, v2)
 }
 
 func Div(x, y Value) Value {
@@ -610,3 +612,64 @@ func (x Value) Clamp(min, max Value) Value {
 	}
 	return x
 }
+
+type Operator func(a, b Value) Value
+
+// float64 mul is the current fastest implementation
+var mulOp = multiplyValueWithFloat64
+
+func init() {
+	fpMode := os.Getenv("FP_MODE")
+	switch fpMode {
+	case "int64":
+		mulOp = multiplyWithInt64
+
+	case "float64":
+		mulOp = multiplyValueWithFloat64
+
+	case "mathbig":
+		mulOp = multiplyBigInt
+
+	}
+
+}
+
+func multiplyBigInt(a, b Value) Value {
+	bigA := big.NewInt(int64(a))
+	bigB := big.NewInt(int64(b))
+	result := new(big.Int).Mul(bigA, bigB)
+
+	// 恢復精度 (除以 10^8)
+	scalingFactor := big.NewInt(1e8)
+	result.Div(result, scalingFactor)
+
+	return Value(result.Int64())
+}
+
+func multiplyValueWithFloat64(x, y Value) Value {
+	return NewFromFloat(x.Float64() * y.Float64())
+}
+
+func multiplyWithInt64(a, b Value) Value {
+	const scaleFactor = 100000000
+
+	highA := a / 10000
+	lowA := a % 10000
+	highB := b / 10000
+	lowB := b % 10000
+
+	highResult := highA * highB
+	midResult1 := highA * lowB
+	midResult2 := lowA * highB
+	lowResult := (lowA * lowB) / 10000
+
+	// merge result
+	result := highResult*scaleFactor + (midResult1+midResult2)*10000 + lowResult
+
+	// add the remainder
+	result += scaleFactor / 2
+
+	result /= scaleFactor
+
+	return result
+}