Golang math.Round is calculate correct but return wrong value

Go version

go version go1.23.4 windows/amd64

Output of go env in your module/workspace:

set GO111MODULE=on
set GOARCH=amd64
set GOBIN=
set GOCACHE=D:\Enviornment\GO\src\cache
set GOENV=C:\Users\admin\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=D:\Workspace\GO\pkg\mod
set GONOPROXY=gitee.com
set GONOSUMDB=gitee.com
set GOOS=windows
set GOPATH=D:\Workspace\GO
set GOPRIVATE=gitee.com
set GOPROXY=https://goproxy.cn,direct
set GOROOT=D:\Enviornment\GO
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLCHAIN=auto
set GOTOOLDIR=D:\Enviornment\GO\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.23.4
set GODEBUG=
set GOTELEMETRY=local
set GOTELEMETRYDIR=C:\Users\admin\AppData\Roaming\go\telemetry
set GCCGO=gccgo
set GOAMD64=v1
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=D:\Workspace\GO\src\gitlab\readboy\wrong-question-book\go.mod
set GOWORK=
set CGO_CFLAGS=-O2 -g
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-O2 -g
set CGO_FFLAGS=-O2 -g
set CGO_LDFLAGS=-O2 -g
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=C:\Users\admin\AppData\Local\Temp\go-build2290248184=/tmp/go-build -gno-record-gcc-switches

What did you do?

package utils_test

import (
    "fmt"
    "math"
    "testing"
)

func TestToPercentage(t *testing.T) {
    testcases := []struct {
        value float64
        digit int
        want  string
    }{
        // {0.123456, 2, "12.35%"},
        // {0, 0, "0"},
        // {0.123456, 4, "12.3456%"},
        // {0.5, 0, "50%"},
        // {0.5, 1, "50%"},
        // {1, 0, "100%"},
        {0.5666666666666667, 0, "57%"},
    }
    for idx, tc := range testcases {
        got1 := ToPercentage(tc.value, tc.digit)
        got2 := ToPercentage2(tc.value, tc.digit)
        if got1 != got2 {
            t.Errorf("%d. ToPercentage(%v) = %s, value1: %s, value2: %s", idx, tc.value, tc.want, got1, got2)
        }
    }
}

func ToPercentage(value float64, n int) string {
    if value == 0 {
        return "0"
    }
    r2 := fmt.Sprintf("%v%%", math.Round(value*math.Pow10(n+2))/math.Pow10(n))
    return r2
}

func ToPercentage2(value float64, n int) string {
    if value == 0 {
        return "0"
    }
    return fmt.Sprintf("%v%%", Round(value, n+2)*100)
}

func Round(value float64, digit int) float64 {
    return math.Round(value*math.Pow10(digit)) / math.Pow10(digit)
}

What did you see happen?

--- FAIL: TestToPercentage (0.00s)
    d:\Workspace\GO\src\gitlab\readboy\wrong-question-book\utils\ratio_test.go:27: 0. ToPercentage(0.5666666666666667) = 57%, value1: 57%, value2: 56.99999999999999%
FAIL
FAIL    wrong-question-book/utils   0.652s
FAIL

What did you expect to see?

the testcase is correct

Comment From: seankhliao

I believe this is correct due to how floating point represents numbers.

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