log10

README

Package log10 calculates log base 10 of an integer, fast.

It is inspired by Daniel Lemire's blog post on this topic.

TODO:

• Add implementations for other bit widths.
• Teach the compiler some tricks to make this faster yet.

Documentation

Overview

Package log10 calculates log base 10 of an integer. This is a simple task. This package focuses on performance, as there are non-obvious techniques for speed.

Index

• func Uint32(x uint32) int

Examples

• Uint32

Functions

func Uint32

func Uint32(x uint32) int

Uint32 returns the number of digits required to hold the base 10 representation of x. As a special case, Uint32(0) == 1.

Note that if you are making a byte buffer for a base 10 representation of x, you will often get better results by calling make with a large-enough constant. Be sure to benchmark both approaches.

Implementation inspired by https://lemire.me/blog/2021/05/28/computing-the-number-of-digits-of-an-integer-quickly/#comment-585476 and tweaked for the Go compiler.

Example

package main

import (
	"fmt"

	"github.com/josharian/log10"
)

func main() {
	examples := []uint32{0, 1, 9, 10, 11}
	for _, e := range examples {
		fmt.Printf("log10.Uint32(%d) = %d\n", e, log10.Uint32(e))
	}
}

Output:

log10.Uint32(0) = 1
log10.Uint32(1) = 1
log10.Uint32(9) = 1
log10.Uint32(10) = 2
log10.Uint32(11) = 2