Function log_decimal128

datafusion/functions/src/math/log.rs:148–161

Calculate logarithm for Decimal128 values. For integer bases >= 2 with zero scale, return an exact integer log when the value is a perfect power of the base. Otherwise falls back to f64 computation.

(value: i128, scale: i8, base: f64)

/// For integer bases >= 2 with zero scale, return an exact integer log when the
/// value is a perfect power of the base. Otherwise falls back to f64 computation.
fn log_decimal128(value: i128, scale: i8, base: f64) -> Result<f64, ArrowError> {
    if scale == 0
        && is_valid_integer_base(base)
        && let Ok(unscaled) = u128::try_from(value)
        && unscaled > 0
    {
        let base_u128 = base as u128;
        let int_log = unscaled.ilog(base_u128);
        if base_u128.checked_pow(int_log) == Some(unscaled) {
            return Ok(int_log as f64);
        }
    }
    decimal_to_f64(value, scale).map(|v| v.log(base))
}

/// Convert a scaled decimal value to f64.
#[inline]