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Adding floats shows unwanted / wrong precision #39546

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factors-prateek opened this issue Jun 12, 2020 · 1 comment
Closed

Adding floats shows unwanted / wrong precision #39546

factors-prateek opened this issue Jun 12, 2020 · 1 comment

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@factors-prateek
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@factors-prateek factors-prateek commented Jun 12, 2020

What version of Go are you using (go version)?

$ go version
go version go1.14.2 darwin/amd64

Does this issue reproduce with the latest release?

Not sure.

What operating system and processor architecture are you using (go env)?

go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/prateek/Library/Caches/go-build"
GOENV="/Users/prateek/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/prateek/Documents/workspace/factors/backend"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/3l/wp0dvd6901q1l1bn_z8bzm1h0000gp/T/go-build389574889=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

package main

import "fmt"

func main() {
    a, b := 2.2, 2.2
    fmt.Println(a + b)

    a, b = 2.2, 2.3
    fmt.Println(a + b)

    a, b = 2.2, 4.4
    fmt.Println(a + b)

    a, b = 1.1, 2.2
    fmt.Println(a + b)
}

What did you expect to see?

4.4
4.5
6.6
3.3

What did you see instead?

4.4
4.5
6.6000000000000005
3.3000000000000003
@ALTree
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@ALTree ALTree commented Jun 12, 2020

Println shows 6.6000000000000005 because it's closer to the actual value of 2.2 + 4.4 in IEEE-754 float64 arithmetic. If you want to truncate the value, use Printf and %f, e.g.

a, b := 2.2, 4.4
fmt.Printf("%.2f", a + b)    // prints 6.60

Closing here, since this is working as intended.

@ALTree ALTree closed this Jun 12, 2020
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