Method log

packages/bigdecimal/index.ts:454–477

(base: number)

  }

  log(base: number): BigDecimal {
    if (this._special === SpecialValue.NAN) return this
    if (this._special === SpecialValue.NEGATIVE_INFINITY) {
      return BigDecimal._create(0n, 0, SpecialValue.NAN, false)
    }
    if (this._special === SpecialValue.POSITIVE_INFINITY) {
      return BigDecimal._create(0n, 0, SpecialValue.POSITIVE_INFINITY, false)
    }
    if (this._mantissa < 0n) {
      return BigDecimal._create(0n, 0, SpecialValue.NAN, false)
    }
    if (this._mantissa === 0n) {
      return BigDecimal._create(0n, 0, SpecialValue.NEGATIVE_INFINITY, false)
    }

    if (base === 10) {
      return this._log10()
    }

    // General case: log_b(x) = log10(x) / log10(b)
    const log10x = this._log10()
    const log10b = new BigDecimal(Math.log10(base))
    return log10x.div(log10b)
  }

  private _log10(): BigDecimal {
    // log10(mantissa * 10^exponent) = log10(mantissa) + exponent