Function log_base_numeric

src/expr/src/scalar/func.rs:1312–1346

(mut a: Numeric, mut b: Numeric)

#[sqlfunc(sqlname = "log", propagates_nulls = true)]
fn log_base_numeric(mut a: Numeric, mut b: Numeric) -> Result<Numeric, EvalError> {
    log_guard_numeric(&a, "log")?;
    log_guard_numeric(&b, "log")?;
    let mut cx = numeric::cx_datum();
    cx.ln(&mut a);
    cx.ln(&mut b);
    cx.div(&mut b, &a);
    if a.is_zero() {
        Err(EvalError::DivisionByZero)
    } else {
        // This division can result in slightly wrong answers due to the
        // limitation of dividing irrational numbers. To correct that, see if
        // rounding off the value from its `numeric::NUMERIC_DATUM_MAX_PRECISION
        // - 1`th position results in an integral value.
        cx.set_precision(usize::from(numeric::NUMERIC_DATUM_MAX_PRECISION - 1))
            .expect("reducing precision below max always succeeds");
        let mut integral_check = b.clone();

        // `reduce` rounds to the context's final digit when the number of
        // digits in its argument exceeds its precision. We've contrived that to
        // happen by shrinking the context's precision by 1.
        cx.reduce(&mut integral_check);

        // Reduced integral values always have a non-negative exponent.
        let mut b = if integral_check.exponent() >= 0 {
            // We believe our result should have been an integral
            integral_check
        } else {
            b
        };

        numeric::munge_numeric(&mut b).unwrap();
        Ok(b)
    }
}

#[sqlfunc(propagates_nulls = true)]
fn power(a: f64, b: f64) -> Result<f64, EvalError> {