jimeh/rands

package rands

import (
    "crypto/rand"
    "fmt"
    "math/big"
)

var ErrInvalidMaxInt = fmt.Errorf("%w: max cannot be less than 1", Err)

// Int generates a random int ranging between 0 and max.
func Int(max int) (int, error) {
    if max < 1 {
        return 0, ErrInvalidMaxInt
    }

    r, err := rand.Int(rand.Reader, big.NewInt(int64(max)))
    if err != nil {
        return 0, err
    }

    return int(r.Int64()), nil
}

// Int64 generates a random int64 ranging between 0 and max.
func Int64(max int64) (int64, error) {
    if max < 1 {
        return 0, ErrInvalidMaxInt
    }

    r, err := rand.Int(rand.Reader, big.NewInt(max))
    if err != nil {
        return 0, err
    }

    return r.Int64(), nil
}