~mendelmaleh/checksum

ref: e71e2f6f91dd70e3fd9fce07672614204fce5348 checksum/utils.go -rw-r--r-- 1.3 KiB
e71e2f6fMendel E Initial commit 1 year, 3 months ago
                                                                                
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package checksum

import (
	"fmt"
	"math"
)

// IterInt iterates smallest to largest, over each decimal digit in num,
// and sets fn(index, digit, checksum) as the new sum, and returns it.
func IterInt(num int, fn func(i, n, c int) int) (check int) {
	for i, n := 0, num; n > 0; i, n = i+1, n/10 {
		check = fn(i, n%10, check)
	}

	return check
}

// IterOppositeInt iterates largest to smallest, over each decimal digit in num,
// and sets fn(index, digit, checksum) as the new sum, and returns it.
func IterOppositeInt(num int, fn func(i, n, c int) int) (check int) {
	digits := int(math.Log10(float64(num))) + 1

	for i, n := 0, num; i < digits; i++ {
		p := int(math.Pow10(digits - i - 1))
		check, n = fn(i, n/p, check), n%p
	}

	return check
}

// IterString iterates over each decimal digit in num,
// and sets fn(index, digit, checksum) as the new sum, and returns it.
func IterString(num string, fn func(i, n, c int) int) (check int, err error) {
	for _, r := range num {
		if r == ' ' || r == '_' {
			continue
		}

		if r < '0' || '9' < r {
			return 0, fmt.Errorf("can't validate %q, invalid rune %c, should be a number", num, r)
		}
	}

	bnum := []byte(num)
	var index int
	for i := 0; i < len(bnum); i++ {
		r := bnum[len(bnum)-i-1]

		if r == ' ' || r == '_' {
			continue
		}

		check = fn(index, int(r-'0'), check)
		index++
	}

	return
}