clerk/internal/decimal/decimal.go (view raw)
| 1 | package decimal |
| 2 | |
| 3 | import ( |
| 4 | "fmt" |
| 5 | "math/big" |
| 6 | "strings" |
| 7 | ) |
| 8 | |
| 9 | type Decimal struct { |
| 10 | scale int |
| 11 | coeff *big.Int |
| 12 | } |
| 13 | |
| 14 | // Coeff returns the unscaled coefficient (always non-nil for non-zero values). |
| 15 | func (d Decimal) Coeff() *big.Int { return d.coeff } |
| 16 | |
| 17 | // Scale returns the scale (number of fractional digits). |
| 18 | func (d Decimal) Scale() int { return d.scale } |
| 19 | |
| 20 | func FromInt(v int64) Decimal { |
| 21 | if v == 0 { |
| 22 | return Decimal{} |
| 23 | } |
| 24 | return Decimal{coeff: big.NewInt(v)} |
| 25 | } |
| 26 | |
| 27 | func FromString(s string) (Decimal, error) { |
| 28 | original := s |
| 29 | if s == "" { |
| 30 | return Decimal{}, fmt.Errorf("can't convert %s to decimal", original) |
| 31 | } |
| 32 | |
| 33 | sign := 1 |
| 34 | if s[0] == '+' || s[0] == '-' { |
| 35 | if s[0] == '-' { |
| 36 | sign = -1 |
| 37 | } |
| 38 | s = s[1:] |
| 39 | } |
| 40 | |
| 41 | if s == "" { |
| 42 | return Decimal{}, fmt.Errorf("can't convert %s to decimal", original) |
| 43 | } |
| 44 | |
| 45 | firstDot := strings.IndexByte(s, '.') |
| 46 | lastDot := strings.LastIndexByte(s, '.') |
| 47 | if firstDot != lastDot { |
| 48 | return Decimal{}, fmt.Errorf("can't convert %s to decimal", original) |
| 49 | } |
| 50 | |
| 51 | intPart := s |
| 52 | fracPart := "" |
| 53 | if firstDot >= 0 { |
| 54 | intPart = s[:firstDot] |
| 55 | fracPart = s[firstDot+1:] |
| 56 | } |
| 57 | |
| 58 | if len(intPart)+len(fracPart) == 0 { |
| 59 | return Decimal{}, fmt.Errorf("can't convert %s to decimal", original) |
| 60 | } |
| 61 | |
| 62 | for i := 0; i < len(intPart); i++ { |
| 63 | if intPart[i] < '0' || intPart[i] > '9' { |
| 64 | return Decimal{}, fmt.Errorf("can't convert %s to decimal", original) |
| 65 | } |
| 66 | } |
| 67 | for i := 0; i < len(fracPart); i++ { |
| 68 | if fracPart[i] < '0' || fracPart[i] > '9' { |
| 69 | return Decimal{}, fmt.Errorf("can't convert %s to decimal", original) |
| 70 | } |
| 71 | } |
| 72 | |
| 73 | coeffDigits := intPart + fracPart |
| 74 | coeff := new(big.Int) |
| 75 | if _, ok := coeff.SetString(coeffDigits, 10); !ok { |
| 76 | return Decimal{}, fmt.Errorf("can't convert %s to decimal", original) |
| 77 | } |
| 78 | if sign < 0 && coeff.Sign() != 0 { |
| 79 | coeff.Neg(coeff) |
| 80 | } |
| 81 | |
| 82 | out := Decimal{coeff: coeff, scale: len(fracPart)} |
| 83 | return out.normalized(), nil |
| 84 | } |
| 85 | |
| 86 | func (d Decimal) String() string { |
| 87 | if d.coeff == nil || d.coeff.Sign() == 0 { |
| 88 | return "0" |
| 89 | } |
| 90 | |
| 91 | abs := new(big.Int).Set(d.coeff) |
| 92 | sign := "" |
| 93 | if abs.Sign() < 0 { |
| 94 | sign = "-" |
| 95 | abs.Abs(abs) |
| 96 | } |
| 97 | |
| 98 | digits := abs.String() |
| 99 | if d.scale == 0 { |
| 100 | return sign + digits |
| 101 | } |
| 102 | |
| 103 | if len(digits) <= d.scale { |
| 104 | digits = strings.Repeat("0", d.scale-len(digits)+1) + digits |
| 105 | } |
| 106 | split := len(digits) - d.scale |
| 107 | return sign + digits[:split] + "." + digits[split:] |
| 108 | } |
| 109 | |
| 110 | func (d Decimal) Neg() Decimal { |
| 111 | if d.coeff == nil || d.coeff.Sign() == 0 { |
| 112 | return Decimal{} |
| 113 | } |
| 114 | return Decimal{coeff: new(big.Int).Neg(d.coeff), scale: d.scale} |
| 115 | } |
| 116 | |
| 117 | func (d Decimal) Sub(other Decimal) Decimal { return d.Add(other.Neg()) } |
| 118 | func (d Decimal) Add(other Decimal) Decimal { |
| 119 | a, b, scale := align(d, other) |
| 120 | sum := new(big.Int).Add(a, b) |
| 121 | return Decimal{coeff: sum, scale: scale}.normalized() |
| 122 | } |
| 123 | |
| 124 | func (d Decimal) Mul(other Decimal) Decimal { |
| 125 | if d.IsZero() || other.IsZero() { |
| 126 | return Decimal{} |
| 127 | } |
| 128 | product := new(big.Int).Mul(d.coeffOrZero(), other.coeffOrZero()) |
| 129 | return Decimal{coeff: product, scale: d.scale + other.scale}.normalized() |
| 130 | } |
| 131 | |
| 132 | func (d Decimal) Cmp(other Decimal) int { |
| 133 | a, b, _ := align(d, other) |
| 134 | return a.Cmp(b) |
| 135 | } |
| 136 | |
| 137 | func (d Decimal) Equal(other Decimal) bool { |
| 138 | return d.Cmp(other) == 0 |
| 139 | } |
| 140 | |
| 141 | func (d Decimal) IsZero() bool { |
| 142 | return d.coeff == nil || d.coeff.Sign() == 0 |
| 143 | } |
| 144 | |
| 145 | func align(a, b Decimal) (aCoeff *big.Int, bCoeff *big.Int, scale int) { |
| 146 | scale = max(b.scale, a.scale) |
| 147 | |
| 148 | aCoeff = a.coeffOrZero() |
| 149 | bCoeff = b.coeffOrZero() |
| 150 | if delta := scale - a.scale; delta > 0 { |
| 151 | aCoeff.Mul(aCoeff, pow10(delta)) |
| 152 | } |
| 153 | if delta := scale - b.scale; delta > 0 { |
| 154 | bCoeff.Mul(bCoeff, pow10(delta)) |
| 155 | } |
| 156 | return aCoeff, bCoeff, scale |
| 157 | } |
| 158 | |
| 159 | func (d Decimal) coeffOrZero() *big.Int { |
| 160 | if d.coeff == nil { |
| 161 | return new(big.Int) |
| 162 | } |
| 163 | return new(big.Int).Set(d.coeff) |
| 164 | } |
| 165 | |
| 166 | func (d Decimal) normalized() Decimal { |
| 167 | if d.coeff == nil || d.coeff.Sign() == 0 { |
| 168 | return Decimal{} |
| 169 | } |
| 170 | if d.scale == 0 { |
| 171 | return Decimal{coeff: new(big.Int).Set(d.coeff)} |
| 172 | } |
| 173 | |
| 174 | sign := d.coeff.Sign() |
| 175 | abs := new(big.Int).Abs(d.coeff) |
| 176 | ten := big.NewInt(10) |
| 177 | rem := new(big.Int) |
| 178 | for d.scale > 0 { |
| 179 | quotient, _ := new(big.Int).QuoRem(abs, ten, rem) |
| 180 | if rem.Sign() != 0 { |
| 181 | break |
| 182 | } |
| 183 | abs = quotient |
| 184 | d.scale-- |
| 185 | } |
| 186 | |
| 187 | if sign < 0 { |
| 188 | abs.Neg(abs) |
| 189 | } |
| 190 | return Decimal{coeff: abs, scale: d.scale} |
| 191 | } |
| 192 | |
| 193 | func pow10(n int) *big.Int { |
| 194 | if n <= 0 { |
| 195 | return big.NewInt(1) |
| 196 | } |
| 197 | return new(big.Int).Exp(big.NewInt(10), big.NewInt(int64(n)), nil) |
| 198 | } |