A simple version of the unix utility "cksum" in Go

cksum.go

package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
)

// A simple version of the unix utility "cksum" in Go
// Usage: cksum <file> <file> <file>
// Prints out <checksum> <length> <filename>
// Public Domain / https://creativecommons.org/publicdomain/zero/1.0/
// contact: [email protected]
// simplicity for learning purpose

func main() {
	tbl := [256]uint32{0x00000000, 0x04C11DB7, 0x09823B6E, 0x0D4326D9,
		0x130476DC, 0x17C56B6B, 0x1A864DB2, 0x1E475005,
		0x2608EDB8, 0x22C9F00F, 0x2F8AD6D6, 0x2B4BCB61,
		0x350C9B64, 0x31CD86D3, 0x3C8EA00A, 0x384FBDBD,
		0x4C11DB70, 0x48D0C6C7, 0x4593E01E, 0x4152FDA9,
		0x5F15ADAC, 0x5BD4B01B, 0x569796C2, 0x52568B75,
		0x6A1936C8, 0x6ED82B7F, 0x639B0DA6, 0x675A1011,
		0x791D4014, 0x7DDC5DA3, 0x709F7B7A, 0x745E66CD,
		0x9823B6E0, 0x9CE2AB57, 0x91A18D8E, 0x95609039,
		0x8B27C03C, 0x8FE6DD8B, 0x82A5FB52, 0x8664E6E5,
		0xBE2B5B58, 0xBAEA46EF, 0xB7A96036, 0xB3687D81,
		0xAD2F2D84, 0xA9EE3033, 0xA4AD16EA, 0xA06C0B5D,
		0xD4326D90, 0xD0F37027, 0xDDB056FE, 0xD9714B49,
		0xC7361B4C, 0xC3F706FB, 0xCEB42022, 0xCA753D95,
		0xF23A8028, 0xF6FB9D9F, 0xFBB8BB46, 0xFF79A6F1,
		0xE13EF6F4, 0xE5FFEB43, 0xE8BCCD9A, 0xEC7DD02D,
		0x34867077, 0x30476DC0, 0x3D044B19, 0x39C556AE,
		0x278206AB, 0x23431B1C, 0x2E003DC5, 0x2AC12072,
		0x128E9DCF, 0x164F8078, 0x1B0CA6A1, 0x1FCDBB16,
		0x018AEB13, 0x054BF6A4, 0x0808D07D, 0x0CC9CDCA,
		0x7897AB07, 0x7C56B6B0, 0x71159069, 0x75D48DDE,
		0x6B93DDDB, 0x6F52C06C, 0x6211E6B5, 0x66D0FB02,
		0x5E9F46BF, 0x5A5E5B08, 0x571D7DD1, 0x53DC6066,
		0x4D9B3063, 0x495A2DD4, 0x44190B0D, 0x40D816BA,
		0xACA5C697, 0xA864DB20, 0xA527FDF9, 0xA1E6E04E,
		0xBFA1B04B, 0xBB60ADFC, 0xB6238B25, 0xB2E29692,
		0x8AAD2B2F, 0x8E6C3698, 0x832F1041, 0x87EE0DF6,
		0x99A95DF3, 0x9D684044, 0x902B669D, 0x94EA7B2A,
		0xE0B41DE7, 0xE4750050, 0xE9362689, 0xEDF73B3E,
		0xF3B06B3B, 0xF771768C, 0xFA325055, 0xFEF34DE2,
		0xC6BCF05F, 0xC27DEDE8, 0xCF3ECB31, 0xCBFFD686,
		0xD5B88683, 0xD1799B34, 0xDC3ABDED, 0xD8FBA05A,
		0x690CE0EE, 0x6DCDFD59, 0x608EDB80, 0x644FC637,
		0x7A089632, 0x7EC98B85, 0x738AAD5C, 0x774BB0EB,
		0x4F040D56, 0x4BC510E1, 0x46863638, 0x42472B8F,
		0x5C007B8A, 0x58C1663D, 0x558240E4, 0x51435D53,
		0x251D3B9E, 0x21DC2629, 0x2C9F00F0, 0x285E1D47,
		0x36194D42, 0x32D850F5, 0x3F9B762C, 0x3B5A6B9B,
		0x0315D626, 0x07D4CB91, 0x0A97ED48, 0x0E56F0FF,
		0x1011A0FA, 0x14D0BD4D, 0x19939B94, 0x1D528623,
		0xF12F560E, 0xF5EE4BB9, 0xF8AD6D60, 0xFC6C70D7,
		0xE22B20D2, 0xE6EA3D65, 0xEBA91BBC, 0xEF68060B,
		0xD727BBB6, 0xD3E6A601, 0xDEA580D8, 0xDA649D6F,
		0xC423CD6A, 0xC0E2D0DD, 0xCDA1F604, 0xC960EBB3,
		0xBD3E8D7E, 0xB9FF90C9, 0xB4BCB610, 0xB07DABA7,
		0xAE3AFBA2, 0xAAFBE615, 0xA7B8C0CC, 0xA379DD7B,
		0x9B3660C6, 0x9FF77D71, 0x92B45BA8, 0x9675461F,
		0x8832161A, 0x8CF30BAD, 0x81B02D74, 0x857130C3,
		0x5D8A9099, 0x594B8D2E, 0x5408ABF7, 0x50C9B640,
		0x4E8EE645, 0x4A4FFBF2, 0x470CDD2B, 0x43CDC09C,
		0x7B827D21, 0x7F436096, 0x7200464F, 0x76C15BF8,
		0x68860BFD, 0x6C47164A, 0x61043093, 0x65C52D24,
		0x119B4BE9, 0x155A565E, 0x18197087, 0x1CD86D30,
		0x029F3D35, 0x065E2082, 0x0B1D065B, 0x0FDC1BEC,
		0x3793A651, 0x3352BBE6, 0x3E119D3F, 0x3AD08088,
		0x2497D08D, 0x2056CD3A, 0x2D15EBE3, 0x29D4F654,
		0xC5A92679, 0xC1683BCE, 0xCC2B1D17, 0xC8EA00A0,
		0xD6AD50A5, 0xD26C4D12, 0xDF2F6BCB, 0xDBEE767C,
		0xE3A1CBC1, 0xE760D676, 0xEA23F0AF, 0xEEE2ED18,
		0xF0A5BD1D, 0xF464A0AA, 0xF9278673, 0xFDE69BC4,
		0x89B8FD09, 0x8D79E0BE, 0x803AC667, 0x84FBDBD0,
		0x9ABC8BD5, 0x9E7D9662, 0x933EB0BB, 0x97FFAD0C,
		0xAFB010B1, 0xAB710D06, 0xA6322BDF, 0xA2F33668,
		0xBCB4666D, 0xB8757BDA, 0xB5365D03, 0xB1F740B4}

	for i := 1; i < len(os.Args); i++ {
		rd, err := os.Open(os.Args[i])
		if err != nil {
			fmt.Println(err)
			os.Exit(-1)
		}
		bufr := bufio.NewReader(rd)
		crc := uint32(0)

		length := 0
		for {
			v, err := bufr.ReadByte()
			if err != nil {
				if err != io.EOF {
					fmt.Println(err)
					os.Exit(-1)
				} else {
					break
				}
			}
			crc = tbl[byte(crc>>24)^v] ^ (crc << 8)
			length++
		}

		for extra := uint32(length); extra > 0; extra >>= 8 {
			crc = (crc << 8) ^ tbl[byte(crc>>24)^byte(extra&0xff)]
		}

		crc = ^crc
		fmt.Println(crc, length, os.Args[i])
		rd.Close()
	}
}