A little program to show the innards of a floating point number.

fpshow.go

package main

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

func main() {
	v := os.Args[1]

	num := big.NewInt(0)
	mark := -1
	for i, c := range v {
		if c == '.' {
			mark = i
		}

		digit := c - '0'

		num = num.Mul(num, big.NewInt(10))
		num = num.Add(num, big.NewInt(int64(digit)))
	}

	den := big.NewInt(1)
	if mark > -1 {
		den = den.Exp(big.NewInt(10), big.NewInt(int64(len(v)-mark-1)), nil)
	}

	rat := big.NewRat(0, 1)
	rat = rat.SetFrac(num, den)

	f64, _ := rat.Float64()
	fmt.Printf("%064b\n", math.Float64bits(f64))
}