Function NumDigits

table.go:62–107

NumDigits returns the number of decimal digits of b.

(b *BigInt)

// NumDigits returns the number of decimal digits of b.
func NumDigits(b *BigInt) int64 {
	bl := b.BitLen()
	if bl == 0 {
		return 1
	}

	if bl <= digitsTableSize {
		val := &digitsLookupTable[bl]
		// In general, we either have val.digits or val.digits+1 digits and we have
		// to compare with the border value. But that's not true for all values of
		// bl: in particular, if bl+1 maps to the same number of digits, then we
		// know for sure we have val.digits and we can skip the comparison.
		// This is the case for about 2 out of 3 values.
		if bl < digitsTableSize && digitsLookupTable[bl+1].digits == val.digits {
			return val.digits
		}

		switch b.Sign() {
		case 1:
			if b.Cmp(&val.border) < 0 {
				return val.digits
			}
		case -1:
			if b.Cmp(&val.nborder) > 0 {
				return val.digits
			}
		}
		return val.digits + 1
	}

	n := int64(float64(bl) / digitsToBitsRatio)
	var tmp BigInt
	e := tableExp10(n, &tmp)
	var a *BigInt
	if b.Sign() < 0 {
		var tmpA BigInt
		a = &tmpA
		a.Abs(b)
	} else {
		a = b
	}
	if a.Cmp(e) >= 0 {
		n++
	}
	return n
}

// powerTenTableSize is the magnitude of the maximum power of 10 exponent that
// is stored in the pow10LookupTable. For instance, if the powerTenTableSize