Golang Dec.SetScale方法代码示例

// ParseQuantity turns str into a Quantity, or returns an error.
func ParseQuantity(str string) (*Quantity, error) {
	parts := splitRE.FindStringSubmatch(strings.TrimSpace(str))
	// regexp returns are entire match, followed by an entry for each () section.
	if len(parts) != 3 {
		return nil, ErrFormatWrong
	}

	amount := new(inf.Dec)
	if _, ok := amount.SetString(parts[1]); !ok {
		return nil, ErrNumeric
	}

	base, exponent, format, ok := quantitySuffixer.interpret(suffix(parts[2]))
	if !ok {
		return nil, ErrSuffix
	}

	// So that no one but us has to think about suffixes, remove it.
	if base == 10 {
		amount.SetScale(amount.Scale() + Scale(exponent).infScale())
	} else if base == 2 {
		// numericSuffix = 2 ** exponent
		numericSuffix := big.NewInt(1).Lsh(bigOne, uint(exponent))
		ub := amount.UnscaledBig()
		amount.SetUnscaledBig(ub.Mul(ub, numericSuffix))
	}

	// Cap at min/max bounds.
	sign := amount.Sign()
	if sign == -1 {
		amount.Neg(amount)
	}

	// This rounds non-zero values up to the minimum representable value, under the theory that
	// if you want some resources, you should get some resources, even if you asked for way too small
	// of an amount.  Arguably, this should be inf.RoundHalfUp (normal rounding), but that would have
	// the side effect of rounding values < .5n to zero.
	if v, ok := amount.Unscaled(); v != int64(0) || !ok {
		amount.Round(amount, Nano.infScale(), inf.RoundUp)
	}

	// The max is just a simple cap.
	if amount.Cmp(maxAllowed) > 0 {
		amount.Set(maxAllowed)
	}
	if format == BinarySI && amount.Cmp(decOne) < 0 && amount.Cmp(decZero) > 0 {
		// This avoids rounding and hopefully confusion, too.
		format = DecimalSI
	}
	if sign == -1 {
		amount.Neg(amount)
	}

	return &Quantity{amount, format}, nil
}

// AsDec returns an inf.Dec representation of this value.
func (a int64Amount) AsDec() *inf.Dec {
	var base inf.Dec
	base.SetUnscaled(a.value)
	base.SetScale(inf.Scale(-a.scale))
	return &base
}

// ParseQuantity turns str into a Quantity, or returns an error.
func ParseQuantity(str string) (Quantity, error) {
	if len(str) == 0 {
		return Quantity{}, ErrFormatWrong
	}
	if str == "0" {
		return Quantity{Format: DecimalSI, s: str}, nil
	}

	positive, value, num, denom, suf, err := parseQuantityString(str)
	if err != nil {
		return Quantity{}, err
	}

	base, exponent, format, ok := quantitySuffixer.interpret(suffix(suf))
	if !ok {
		return Quantity{}, ErrSuffix
	}

	precision := int32(0)
	scale := int32(0)
	mantissa := int64(1)
	switch format {
	case DecimalExponent, DecimalSI:
		scale = exponent
		precision = maxInt64Factors - int32(len(num)+len(denom))
	case BinarySI:
		scale = 0
		switch {
		case exponent >= 0 && len(denom) == 0:
			// only handle positive binary numbers with the fast path
			mantissa = int64(int64(mantissa) << uint64(exponent))
			// 1Mi (2^20) has ~6 digits of decimal precision, so exponent*3/10 -1 is roughly the precision
			precision = 15 - int32(len(num)) - int32(float32(exponent)*3/10) - 1
		default:
			precision = -1
		}
	}

	if precision >= 0 {
		// if we have a denominator, shift the entire value to the left by the number of places in the
		// denominator
		scale -= int32(len(denom))
		if scale >= int32(Nano) {
			shifted := num + denom

			var value int64
			value, err := strconv.ParseInt(shifted, 10, 64)
			if err != nil {
				return Quantity{}, ErrNumeric
			}
			if result, ok := int64Multiply(value, int64(mantissa)); ok {
				if !positive {
					result = -result
				}
				// if the number is in canonical form, reuse the string
				switch format {
				case BinarySI:
					if exponent%10 == 0 && (value&0x07 != 0) {
						return Quantity{i: int64Amount{value: result, scale: Scale(scale)}, Format: format, s: str}, nil
					}
				default:
					if scale%3 == 0 && !strings.HasSuffix(shifted, "000") && shifted[0] != '0' {
						return Quantity{i: int64Amount{value: result, scale: Scale(scale)}, Format: format, s: str}, nil
					}
				}
				return Quantity{i: int64Amount{value: result, scale: Scale(scale)}, Format: format}, nil
			}
		}
	}

	amount := new(inf.Dec)
	if _, ok := amount.SetString(value); !ok {
		return Quantity{}, ErrNumeric
	}

	// So that no one but us has to think about suffixes, remove it.
	if base == 10 {
		amount.SetScale(amount.Scale() + Scale(exponent).infScale())
	} else if base == 2 {
		// numericSuffix = 2 ** exponent
		numericSuffix := big.NewInt(1).Lsh(bigOne, uint(exponent))
		ub := amount.UnscaledBig()
		amount.SetUnscaledBig(ub.Mul(ub, numericSuffix))
	}

	// Cap at min/max bounds.
	sign := amount.Sign()
	if sign == -1 {
		amount.Neg(amount)
	}

	// This rounds non-zero values up to the minimum representable value, under the theory that
	// if you want some resources, you should get some resources, even if you asked for way too small
	// of an amount.  Arguably, this should be inf.RoundHalfUp (normal rounding), but that would have
	// the side effect of rounding values < .5n to zero.
	if v, ok := amount.Unscaled(); v != int64(0) || !ok {
		amount.Round(amount, Nano.infScale(), inf.RoundUp)
	}

//.........这里部分代码省略.........