Function quantize_block_large 

pub fn quantize_block_large(
    dct_coeffs: &[f32],
    weights: &[f32],
    qac_qm: f32,
    thresholds: &[f32; 4],
    grid_width: usize,
    grid_height: usize,
    llf_x: usize,
    llf_y: usize,
    output: &mut [i32],
)

Quantize AC coefficients for a large block (DCT16+) to a flat output buffer.

For each coefficient at position (y, x) in the grid: val = dct_coeffs[ygrid_width + x] / weights[ygrid_width + x] * qac_qm if y < llf_y && x < llf_x: output 0 (LLF handled separately) elif |val| < threshold[quadrant]: output 0 else: output round_ties_even(val) as i32

grid_width MUST be a multiple of 8. thresholds[0..4] map to quadrants: [top-left, top-right, bottom-left, bottom-right] where the split is at grid_height/2 and grid_width/2.