fastnum 0.7.4

Fast decimal numbers library
Documentation 
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use core::cmp::Ordering;

use crate::{
    bint::UInt,
    decimal::{
        dec::{
            math::add::add_abs,
            scale::{extend_scale_to, rescale},
            utils,
        },
        Decimal,
    },
};

type D<const N: usize> = Decimal<N>;

#[inline(never)]
pub(crate) const fn sub<const N: usize>(lhs: D<N>, rhs: D<N>) -> D<N> {
    if lhs.is_nan() {
        return lhs.compound(&rhs).op_invalid();
    }

    if rhs.is_nan() {
        return rhs.compound(&lhs).op_invalid();
    }

    match (lhs.cb.is_negative(), rhs.cb.is_negative()) {
        (false, false) => sub_abs(lhs, rhs),
        (true, true) => sub_abs(rhs.neg(), lhs.neg()),
        (false, true) => add_abs(lhs, rhs.neg()),
        (true, false) => add_abs(lhs.neg(), rhs).neg(),
    }
}

#[inline(always)]
pub(crate) const fn sub_abs<const N: usize>(mut lhs: D<N>, mut rhs: D<N>) -> D<N> {
    debug_assert!(!lhs.is_negative() && !rhs.is_negative());

    if lhs.is_infinite() && rhs.is_infinite() {
        return D::SIGNALING_NAN.set_ctx(lhs.context()).compound(&rhs);
    } else if lhs.is_infinite() {
        return lhs.compound(&rhs);
    } else if rhs.is_infinite() {
        return rhs.compound(&lhs).neg();
    }

    if rhs.is_zero() {
        return extend_scale_to(lhs, rhs.cb.get_scale()).compound(&rhs);
    }

    if lhs.is_zero() {
        return extend_scale_to(rhs, lhs.cb.get_scale())
            .compound(&lhs)
            .neg();
    }

    match lhs.cb.scale_cmp(&rhs.cb) {
        Ordering::Equal => sub_aligned(lhs, rhs),
        Ordering::Less => {
            rescale(&mut lhs, rhs.cb.get_scale());

            if lhs.is_op_clamped() {
                rescale(&mut rhs, lhs.cb.get_scale());
                sub_aligned(lhs, rhs)
            } else {
                sub_aligned(lhs, rhs)
            }
        }
        Ordering::Greater => {
            rescale(&mut rhs, lhs.cb.get_scale());

            if rhs.is_op_clamped() {
                rescale(&mut lhs, rhs.cb.get_scale());
                sub_aligned(lhs, rhs)
            } else {
                sub_aligned(lhs, rhs)
            }
        }
    }
}

#[inline(always)]
const fn sub_aligned<const N: usize>(mut lhs: D<N>, mut rhs: D<N>) -> D<N> {
    debug_assert!(lhs.cb.get_scale() == rhs.cb.get_scale());

    match lhs.digits.cmp(&rhs.digits) {
        Ordering::Less => {
            rhs.digits = rhs.digits.strict_sub(lhs.digits);
            utils::sub_extra_precision(&mut rhs, &lhs);
            rhs.compound(&lhs).neg()
        }
        Ordering::Equal => {
            lhs.digits = UInt::ZERO;
            utils::sub_extra_precision(&mut lhs, &rhs);
            lhs.compound(&rhs)
        }
        Ordering::Greater => {
            lhs.digits = lhs.digits.strict_sub(rhs.digits);
            utils::sub_extra_precision(&mut lhs, &rhs);
            lhs.compound(&rhs)
        }
    }
}