clerk/internal/decimal/decimal.go (view raw)
Oleksandr Smirnov
Oleksandr Smirnov
olexsmir@gmail.com syntax: respect commodity format; =*; ===; :=, 2 months ago
olexsmir@gmail.com syntax: respect commodity format; =*; ===; :=, 2 months ago
| 1 | package decimal |
| 2 | |
| 3 | import ( |
| 4 | "fmt" |
| 5 | "math/big" |
| 6 | "strconv" |
| 7 | "strings" |
| 8 | ) |
| 9 | |
| 10 | type Decimal struct { |
| 11 | scale int |
| 12 | coeff *big.Int |
| 13 | } |
| 14 | |
| 15 | func FromInt(v int64) Decimal { |
| 16 | if v == 0 { |
| 17 | return Decimal{} |
| 18 | } |
| 19 | return Decimal{coeff: big.NewInt(v)} |
| 20 | } |
| 21 | |
| 22 | func FromString(s string) (Decimal, error) { |
| 23 | original := s |
| 24 | if s == "" { |
| 25 | return Decimal{}, badDecimal(original) |
| 26 | } |
| 27 | |
| 28 | neg := false |
| 29 | if s[0] == '+' || s[0] == '-' { |
| 30 | neg = s[0] == '-' |
| 31 | s = s[1:] |
| 32 | } |
| 33 | |
| 34 | exp := 0 |
| 35 | if e := strings.IndexAny(s, "eE"); e >= 0 { |
| 36 | n, err := strconv.Atoi(s[e+1:]) |
| 37 | if err != nil { |
| 38 | return Decimal{}, badDecimal(original) |
| 39 | } |
| 40 | // bounded so pow10 can't be asked to materialize an astronomically |
| 41 | // large number (e.g. 1E1000000000000) |
| 42 | const maxExp = 10000 |
| 43 | if n > maxExp || n < -maxExp { |
| 44 | return Decimal{}, badDecimal(original) |
| 45 | } |
| 46 | exp = n |
| 47 | s = s[:e] |
| 48 | } |
| 49 | |
| 50 | intPart, fracPart := s, "" |
| 51 | if before, after, ok := strings.Cut(s, "."); ok { |
| 52 | if strings.IndexByte(after, '.') >= 0 { |
| 53 | return Decimal{}, badDecimal(original) |
| 54 | } |
| 55 | intPart, fracPart = before, after |
| 56 | } |
| 57 | |
| 58 | digits := intPart + fracPart |
| 59 | if neg { |
| 60 | digits = "-" + digits |
| 61 | } |
| 62 | coeff, ok := new(big.Int).SetString(digits, 10) |
| 63 | if !ok { |
| 64 | return Decimal{}, badDecimal(original) |
| 65 | } |
| 66 | |
| 67 | scale := len(fracPart) - exp |
| 68 | if scale < 0 { |
| 69 | coeff.Mul(coeff, pow10(-scale)) |
| 70 | scale = 0 |
| 71 | } |
| 72 | return Decimal{coeff: coeff, scale: scale}.normalized(), nil |
| 73 | } |
| 74 | |
| 75 | func badDecimal(s string) error { return fmt.Errorf("can't convert %s to decimal", s) } |
| 76 | |
| 77 | func (d Decimal) String() string { |
| 78 | if d.coeff == nil || d.coeff.Sign() == 0 { |
| 79 | return "0" |
| 80 | } |
| 81 | |
| 82 | abs := new(big.Int).Set(d.coeff) |
| 83 | sign := "" |
| 84 | if abs.Sign() < 0 { |
| 85 | sign = "-" |
| 86 | abs.Abs(abs) |
| 87 | } |
| 88 | |
| 89 | digits := abs.String() |
| 90 | if d.scale == 0 { |
| 91 | return sign + digits |
| 92 | } |
| 93 | |
| 94 | if len(digits) <= d.scale { |
| 95 | digits = strings.Repeat("0", d.scale-len(digits)+1) + digits |
| 96 | } |
| 97 | split := len(digits) - d.scale |
| 98 | return sign + digits[:split] + "." + digits[split:] |
| 99 | } |
| 100 | |
| 101 | // StringFixed returns a string representation with exactly places digits |
| 102 | // after the decimal point. Pads with zeros or truncates as needed. |
| 103 | // decSep and thousandsSep control formatting; zero values mean no custom separator. |
| 104 | func (d Decimal) StringFixed(places int, decSep, thousandsSep byte) string { |
| 105 | var sb strings.Builder |
| 106 | sb.Grow(32) |
| 107 | d.WriteFixed(&sb, places, decSep, thousandsSep) |
| 108 | return sb.String() |
| 109 | } |
| 110 | |
| 111 | // WriteFixed writes a string representation with exactly places digits |
| 112 | // after the decimal point directly into sb. Pads with zeros or truncates |
| 113 | // as needed. decSep and thousandsSep control formatting; zero values mean |
| 114 | // no custom separator. |
| 115 | func (d Decimal) WriteFixed(sb *strings.Builder, places int, decSep, thousandsSep byte) { |
| 116 | if d.IsZero() { |
| 117 | sb.WriteByte('0') |
| 118 | if places > 0 { |
| 119 | if decSep != 0 { |
| 120 | sb.WriteByte(decSep) |
| 121 | } else { |
| 122 | sb.WriteByte('.') |
| 123 | } |
| 124 | for range places { |
| 125 | sb.WriteByte('0') |
| 126 | } |
| 127 | } |
| 128 | return |
| 129 | } |
| 130 | |
| 131 | var digitBuf [128]byte |
| 132 | digits := d.coeff.Append(digitBuf[:0], 10) |
| 133 | |
| 134 | sign := false |
| 135 | if len(digits) > 0 && digits[0] == '-' { |
| 136 | sign = true |
| 137 | digits = digits[1:] |
| 138 | } |
| 139 | |
| 140 | intLen := len(digits) - d.scale |
| 141 | |
| 142 | if sign { |
| 143 | sb.WriteByte('-') |
| 144 | } |
| 145 | |
| 146 | // Integer part |
| 147 | if intLen <= 0 { |
| 148 | sb.WriteByte('0') |
| 149 | } else { |
| 150 | for i := range intLen { |
| 151 | if thousandsSep != 0 && i > 0 && (intLen-i)%3 == 0 { |
| 152 | sb.WriteByte(thousandsSep) |
| 153 | } |
| 154 | sb.WriteByte(digits[i]) |
| 155 | } |
| 156 | } |
| 157 | |
| 158 | // Fractional part |
| 159 | if places > 0 { |
| 160 | if decSep != 0 { |
| 161 | sb.WriteByte(decSep) |
| 162 | } else { |
| 163 | sb.WriteByte('.') |
| 164 | } |
| 165 | |
| 166 | written := 0 |
| 167 | if intLen > 0 { |
| 168 | n := min(d.scale, places) |
| 169 | for i := range n { |
| 170 | sb.WriteByte(digits[intLen+i]) |
| 171 | written++ |
| 172 | } |
| 173 | } else { |
| 174 | leadingZeros := -intLen |
| 175 | for ; written < leadingZeros && written < places; written++ { |
| 176 | sb.WriteByte('0') |
| 177 | } |
| 178 | for i := 0; i < len(digits) && written < places; i++ { |
| 179 | sb.WriteByte(digits[i]) |
| 180 | written++ |
| 181 | } |
| 182 | } |
| 183 | for ; written < places; written++ { |
| 184 | sb.WriteByte('0') |
| 185 | } |
| 186 | } |
| 187 | } |
| 188 | |
| 189 | func (d Decimal) Abs() Decimal { |
| 190 | if d.coeff == nil || d.coeff.Sign() == 0 { |
| 191 | return Decimal{} |
| 192 | } |
| 193 | if d.coeff.Sign() > 0 { |
| 194 | return Decimal{coeff: new(big.Int).Set(d.coeff), scale: d.scale} |
| 195 | } |
| 196 | return Decimal{coeff: new(big.Int).Neg(d.coeff), scale: d.scale} |
| 197 | } |
| 198 | |
| 199 | func (d Decimal) Neg() Decimal { |
| 200 | if d.coeff == nil || d.coeff.Sign() == 0 { |
| 201 | return Decimal{} |
| 202 | } |
| 203 | return Decimal{coeff: new(big.Int).Neg(d.coeff), scale: d.scale} |
| 204 | } |
| 205 | |
| 206 | func (d Decimal) Sub(other Decimal) Decimal { return d.Add(other.Neg()) } |
| 207 | func (d Decimal) Add(other Decimal) Decimal { |
| 208 | a, b, scale := align(d, other) |
| 209 | sum := new(big.Int).Add(a, b) |
| 210 | return Decimal{coeff: sum, scale: scale}.normalized() |
| 211 | } |
| 212 | |
| 213 | func (d Decimal) Mul(other Decimal) Decimal { |
| 214 | if d.IsZero() || other.IsZero() { |
| 215 | return Decimal{} |
| 216 | } |
| 217 | product := new(big.Int).Mul(d.coeffOrZero(), other.coeffOrZero()) |
| 218 | return Decimal{coeff: product, scale: d.scale + other.scale}.normalized() |
| 219 | } |
| 220 | |
| 221 | func (d Decimal) Div(other Decimal) Decimal { |
| 222 | if other.IsZero() { |
| 223 | panic("decimal: division by zero") |
| 224 | } |
| 225 | if d.IsZero() { |
| 226 | return Decimal{} |
| 227 | } |
| 228 | |
| 229 | scale := max(d.scale, other.scale) + 10 |
| 230 | |
| 231 | dCoeff := d.coeffOrZero() |
| 232 | oCoeff := other.coeffOrZero() |
| 233 | |
| 234 | shift := scale + other.scale - d.scale |
| 235 | if shift > 0 { |
| 236 | dCoeff = new(big.Int).Mul(dCoeff, pow10(shift)) |
| 237 | } else if shift < 0 { |
| 238 | oCoeff = new(big.Int).Mul(oCoeff, pow10(-shift)) |
| 239 | } |
| 240 | |
| 241 | quo := new(big.Int).Quo(dCoeff, oCoeff) |
| 242 | return Decimal{coeff: quo, scale: scale}.normalized() |
| 243 | } |
| 244 | |
| 245 | func (d Decimal) Cmp(other Decimal) int { |
| 246 | a, b, _ := align(d, other) |
| 247 | return a.Cmp(b) |
| 248 | } |
| 249 | |
| 250 | func (d Decimal) Equal(other Decimal) bool { |
| 251 | return d.Cmp(other) == 0 |
| 252 | } |
| 253 | |
| 254 | func (d Decimal) IsZero() bool { |
| 255 | return d.coeff == nil || d.coeff.Sign() == 0 |
| 256 | } |
| 257 | |
| 258 | func (d Decimal) coeffOrZero() *big.Int { |
| 259 | if d.coeff == nil { |
| 260 | return new(big.Int) |
| 261 | } |
| 262 | return new(big.Int).Set(d.coeff) |
| 263 | } |
| 264 | |
| 265 | func (d Decimal) normalized() Decimal { |
| 266 | if d.coeff == nil || d.coeff.Sign() == 0 { |
| 267 | return Decimal{} |
| 268 | } |
| 269 | if d.scale == 0 { |
| 270 | return Decimal{coeff: new(big.Int).Set(d.coeff)} |
| 271 | } |
| 272 | |
| 273 | sign := d.coeff.Sign() |
| 274 | abs := new(big.Int).Abs(d.coeff) |
| 275 | ten := big.NewInt(10) |
| 276 | rem := new(big.Int) |
| 277 | for d.scale > 0 { |
| 278 | quotient, _ := new(big.Int).QuoRem(abs, ten, rem) |
| 279 | if rem.Sign() != 0 { |
| 280 | break |
| 281 | } |
| 282 | abs = quotient |
| 283 | d.scale-- |
| 284 | } |
| 285 | |
| 286 | if sign < 0 { |
| 287 | abs.Neg(abs) |
| 288 | } |
| 289 | return Decimal{coeff: abs, scale: d.scale} |
| 290 | } |
| 291 | |
| 292 | func align(a, b Decimal) (aCoeff *big.Int, bCoeff *big.Int, scale int) { |
| 293 | scale = max(b.scale, a.scale) |
| 294 | |
| 295 | aCoeff = a.coeffOrZero() |
| 296 | bCoeff = b.coeffOrZero() |
| 297 | if delta := scale - a.scale; delta > 0 { |
| 298 | aCoeff.Mul(aCoeff, pow10(delta)) |
| 299 | } |
| 300 | if delta := scale - b.scale; delta > 0 { |
| 301 | bCoeff.Mul(bCoeff, pow10(delta)) |
| 302 | } |
| 303 | return aCoeff, bCoeff, scale |
| 304 | } |
| 305 | |
| 306 | func pow10(n int) *big.Int { |
| 307 | if n <= 0 { |
| 308 | return big.NewInt(1) |
| 309 | } |
| 310 | return new(big.Int).Exp(big.NewInt(10), big.NewInt(int64(n)), nil) |
| 311 | } |