123456789bitwise: 0 of 40 (pos0, ntok) cases differ PASSdevice Apple M5: GPU us per dispatch, median of 9 paired rounds of 32 (ref / this) pos0 512 ntok 1 attn 67.41 / 67.15 merge 18.21 / 12.17 pos0 512 ntok 4 attn 116.69 / 116.68 merge 17.55 / 13.90 pos0 2048 ntok 1 attn 51.01 / 51.02 merge 9.94 / 6.21 pos0 2048 ntok 4 attn 192.52 / 192.52 merge 45.81 / 43.33 pos0 8192 ntok 1 attn 51.26 / 51.33 merge 10.15 / 6.23 pos0 8192 ntok 4 attn 195.43 / 195.61 merge 45.72 / 43.73