Unable to calculate math.Mod for numbers larger than 1e+16

[theGreatWhiteShark]

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

$ go version
> go version go1.13.4 darwin/amd64

Does this issue reproduce with the latest release?

jupp

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

go env Output

$ go env

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/X/Library/Caches/go-build"
GOENV="/Users/X/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/X/git/getml/package-pipelines/dependencies/relboost-monitor/Code"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.13.4/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.13.4/libexec/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/wr/bphy451d5zs7ng1vk0ql8csr0000gn/T/go-build813277185=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

package main

import (
	"math"
)

func main() {
	println(math.Mod(1e+16+1, 1e+16))
}

What did you expect to see?

+1.000000e+000

What did you see instead?

+0.000000e+000

For math.Mod(1e+15+1, 1e+15) things are still working fine. I haven't tried figuring out the exact number things start to get wrong.

[ALTree]

Hi,

In IEEE-754 64 bit arithmetic, 1e+16 and 1e+16+1 are the same number (and so their mod is zero). See:

func main() {
	fmt.Println(float64(1e+16) == float64(1e+16+1))  // true
}

Closing here, since this is working as expected.