Function ring::limb::fold_5_bit_windows

pub fn fold_5_bit_windows<R, I: FnOnce(u64) -> R, F: Fn(R, u64) -> R>(
    limbs: &[u64],
    init: I,
    fold: F,
) -> R

Processes limbs as a sequence of 5-bit windows, folding the windows from most significant to least significant and returning the accumulated result. The first window will be mapped by init to produce the initial value for the accumulator. Then f will be called to fold the accumulator and the next window until all windows are processed. When the input’s bit length isn’t divisible by 5, the window passed to init will be partial; all windows passed to fold will be full.

This is designed to avoid leaking the contents of limbs through side channels as long as init and fold are side-channel free.

Panics if limbs is empty.