Support code for tests in confactor/envflags

int-ranges.go

package main

import (
	"fmt"
	"io"
	"math/big"
	"os"
)

func generateIntBounds(w io.Writer) {
	// set variables to upper bound
	var (
		b   byte   = ^byte(0)
		u   uint   = ^uint(0)
		u8  uint8  = ^uint8(0)
		u16 uint16 = ^uint16(0)
		u32 uint32 = ^uint32(0)
		u64 uint64 = ^uint64(0)
		i   int    = int(u >> 1)
		i8  int8   = int8(u8 >> 1)
		i16 int16  = int16(u16 >> 1)
		i32 int32  = int32(u32 >> 1)
		i64 int64  = int64(u64 >> 1)
	)
	fmt.Fprintf(w, "tests := map[string]struct{lowin, highin, lwout, highout string}{\n")
	for _, ptr := range []interface{}{
		&b,
		&u, &u8, &u16, &u32, &u64,
		&i, &i8, &i16, &i32, &i64,
	} {
		v, err := ValueOf(ptr)
		if err != nil {
			panic(err)
		}
		max := v.String()
		signed := v.Set("-"+max) == nil
		lo, li, hi, ho, ok := getIntBounds(max, signed)
		if !ok {
			panic("could not convert bounds")
		}
		fmt.Fprintf(w, "{&%T, %q, %q, %q, %q},\n", ptr, li, hi, lo, ho)
	}
	fmt.Fprintf(w, "}\n")
}

func getIntBounds(max string, signed bool) (lowout, lowin, highin, highout string, ok bool) {
	// use math/big to also generate outer bounds of int64 / uint64
	m1 := big.NewInt(-1)
	p1 := big.NewInt(1)
	tmp := big.NewInt(0)
	highin = max
	lowin = "0"
	if signed {
		tmp, ok = tmp.SetString("-"+highin, 10)
		if !ok {
			return
		}
		tmp = tmp.Add(tmp, m1)
		lowin = tmp.String()
	}
	lowout = tmp.Add(tmp, m1).String()
	tmp, ok = tmp.SetString(highin, 10)
	if !ok {
		return
	}
	highout = tmp.Add(tmp, p1).String()
	return
}

func main() {
	generateIntBounds(os.Stdout)
}