Function shift_operator_row 

pub fn shift_operator_row<F: Field>(
    variant: ShiftVariant,
    amount: usize,
    row: &mut [F],
    psi: &[F],
)

Writes the row of a shift operator table that one (variant, amount) pair contributes.

The row holds, for each bit position, the weight that pair moves there:

    row[j] = sum_k psi(k) * shift-ind_variant(k, j, amount)

This is the one place that says what a variant does to a weight vector:

• Logical left and logical right move the weights and leave zeros behind.
• Arithmetic right piles every weight that falls off the end onto the sign position.
• Rotate wraps them around instead.
• The half-word forms apply the same rule to each 32-bit half, reading only the low 5 bits of the amount.

Arguments

The amount is an index over the reduction’s amount axis rather than a validated Shift amount: that axis spans Word::BITS for every variant, and a half-word variant reads it modulo its own 32-bit width.

Every cell of row is written, so the caller need not zero it first. A caller reading one slice at a time can therefore carry a single scratch row across every pair it visits.

Panics

Panics unless the row and the weights each hold one entry per bit position of a word.