Function Decimal

common.go:105–208

Decimal minifies a given byte slice containing a decimal and removes superfluous characters. It differs from Number in that it does not parse exponents. It does not parse or output exponents. prec is the number of significant digits. When prec is zero it will keep all digits. Only digits after the d

(num []byte, prec int)

// Decimal minifies a given byte slice containing a decimal and removes superfluous characters. It differs from Number in that it does not parse exponents.
// It does not parse or output exponents. prec is the number of significant digits. When prec is zero it will keep all digits. Only digits after the dot can be removed to reach the number of significant digits. Very large number may thus have more significant digits.
func Decimal(num []byte, prec int) []byte {
	if len(num) <= 1 {
		return num
	}

	// omit first + and register mantissa start and end, whether it's negative and the exponent
	neg := false
	start := 0
	dot := -1
	end := len(num)
	if 0 < end && (num[0] == '+' || num[0] == '-') {
		if num[0] == '-' {
			neg = true
		}
		start++
	}
	for i, c := range num[start:] {
		if c == '.' {
			dot = start + i
			break
		}
	}
	if dot == -1 {
		dot = end
	}

	// trim leading zeros but leave at least one digit
	for start < end-1 && num[start] == '0' {
		start++
	}
	// trim trailing zeros
	i := end - 1
	for ; dot < i; i-- {
		if num[i] != '0' {
			end = i + 1
			break
		}
	}
	if i == dot {
		end = dot
		if start == end {
			num[start] = '0'
			return num[start : start+1]
		}
	} else if start == end-1 && num[start] == '0' {
		return num[start:end]
	}

	// apply precision
	if 0 < prec && dot <= start+prec {
		precEnd := start + prec + 1 // include dot
		if dot == start {           // for numbers like .012
			digit := start + 1
			for digit < end && num[digit] == '0' {
				digit++
			}
			precEnd = digit + prec
		}