File size: 20,413 Bytes
78d4fcb
 
f96162c
 
 
 
 
 
 
 
 
ba9df6e
 
 
 
 
 
 
 
 
f96162c
 
 
 
 
 
 
78d4fcb
 
f96162c
 
 
 
 
 
 
 
 
78d4fcb
f96162c
ba9df6e
f96162c
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ba9df6e
f96162c
 
ba9df6e
 
f96162c
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ba9df6e
f96162c
 
 
 
 
 
 
 
 
 
 
 
 
 
 
78d4fcb
 
 
f96162c
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ba9df6e
f96162c
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
78d4fcb
f96162c
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ba9df6e
f96162c
 
 
 
 
 
 
ba9df6e
f96162c
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ba9df6e
f96162c
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ba9df6e
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
f96162c
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ba9df6e
 
 
f96162c
 
 
 
 
 
 
ba9df6e
f96162c
 
 
 
 
 
 
ba9df6e
f96162c
ba9df6e
f96162c
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ba9df6e
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
{% if modeSpec is defined %}
{% set mode = modeSpec %}
{% elif mode is not defined %}
{% set mode = "transpose" %}
{% endif %}
{% set presentScalar = presentScalar | default(inputScalar | default("f32")) %}
{% set presentElement = presentElement | default(presentScalar) %}
{% set packed = packed | default(0) %}
{% set bits = bits | default(0) %}
{% set qmax = qmax | default(0) %}
{% set qmin = qmin | default(0) %}
{% macro flat_index_2d(workgroupSize, name="i", bound="params.count", guardInline=false) %}
{% set wgTerm = workgroupSize ~ "u" if workgroupSize is number else workgroupSize %}
  // 2D-folded flat index: gid.y carries the high bits past the dispatch's
  // per-axis workgroup fold width.
{% if bound == "" %}
  let {{ name }} = gid.x + gid.y * {{ DISPATCH_FOLD_WIDTH }}u * {{ wgTerm }};{% else %}
  let {{ name }} = gid.x + gid.y * {{ DISPATCH_FOLD_WIDTH }}u * {{ wgTerm }};
  if ({{ name }} >= {{ bound }}) { return; }{% endif %}{% endmacro %}
{{ env.wgsl.resourceDeclarations }}
{% if mode == "transpose" %}

const KV_HEADS: u32 = {{ kvNumHeads }}u;
const WG: u32 = {{ copyWorkgroupSize }}u;
{% if presentVec4 %}
// Transpose copy [batch, token, head*headDim] -> present [batch, head, token,
// headDim]. The headDim row is contiguous on both sides and divisible by four,
// so each invocation copies one vec4 along d and adjacent invocations write
// adjacent destination vectors.
const HEAD_DIM_V4: u32 = {{ headDimV4 }}u;
const KV_HIDDEN_V4: u32 = {{ kvHiddenV4 }}u;
{% else %}
const HEAD_DIM: u32 = {{ headDim }}u;
const KV_HIDDEN: u32 = {{ kvHidden }}u;
{% endif %}

@compute @workgroup_size(WG, 1, 1)
fn main(
  @builtin(global_invocation_id) gid: vec3<u32>
) {
{{ flat_index_2d("WG", "index", "") }}
{% if presentVec4 %}
  let total = params.batchSize * KV_HEADS * params.kvSeq * HEAD_DIM_V4;
  if (index >= total) {
    return;
  }
  let d4 = index % HEAD_DIM_V4;
  let token = (index / HEAD_DIM_V4) % params.kvSeq;
  let head = (index / (HEAD_DIM_V4 * params.kvSeq)) % KV_HEADS;
  let batch = index / (HEAD_DIM_V4 * params.kvSeq * KV_HEADS);
  let packed = (batch * params.kvSeq + token) * KV_HIDDEN_V4 + head * HEAD_DIM_V4 + d4;
  present_key[index] = {{ presentElement }}(key[packed]);
  present_value[index] = {{ presentElement }}(value[packed]);
{% else %}
  let total = params.batchSize * KV_HEADS * params.kvSeq * HEAD_DIM;
  if (index >= total) {
    return;
  }
  let d = index % HEAD_DIM;
  let token = (index / HEAD_DIM) % params.kvSeq;
  let head = (index / (HEAD_DIM * params.kvSeq)) % KV_HEADS;
  let batch = index / (HEAD_DIM * params.kvSeq * KV_HEADS);
  let packed_index = (batch * params.kvSeq + token) * KV_HIDDEN + head * HEAD_DIM + d;
  present_key[index] = {{ presentScalar }}(key[packed_index]);
  present_value[index] = {{ presentScalar }}(value[packed_index]);
{% endif %}
}
{% else %}

{% set shareAppend = mode == "merge_share" and shareRegion == "append" %}
{% set shiftRegion = shiftRegion | default("all") %}
{% set shiftRetainOnly = mode == "window_shift" and shiftRegion == "shift" %}
{% set cooperativeCopy = device.adapterInfo.vendor != "apple" %}
{% set cooperativeMerge = cooperativeCopy or shareAppend %}
{% set cooperativeMode = cooperativeMerge and (mode == "copy" or mode == "merge" or mode == "merge_share") %}
{% set needsGid = not cooperativeMode or (shareAppend and not cooperativeCopy) %}
{% if mode == "copy" %}
// Copy the existing BNSH cache unchanged. Compression changes only the number
// of stored words per row.
{% elif mode == "merge" %}
// Copy the past BNSH cache, then append new BSH K/V tokens into the present cache.
{% elif mode == "merge_share" %}
// Buffer-sharing append: past and present share the full-capacity BNSH stride.
// Rows outside each batch's append window [seqlens_k[b]+1-keySeq, seqlens_k[b]+1)
// are an identity copy of the past cache; rows inside it come from the new BSH
// K/V (K optionally rotated at its absolute position).
// The append and retain passes own disjoint ranges, so their order is immaterial.
{% elif mode == "build" %}
// Build a BNSH cache from new BSH K/V, optionally applying K RMSNorm and rotary.
{% elif mode == "window_shift" %}
// Windowed cache: compact the surviving past rows down by the eviction count and
// append the new BSH K/V, keeping the most recent min(T, capacity) tokens
// contiguous at rows [0, L). Reads past, writes present (distinct buffers).
{% elif mode == "append_quant" %}
// Quantize new BSH K/V into an existing buffer-sharing INT8 BNSH cache. The
// active sequence end comes from seqlens_k; the physical cache stride remains
// the full present-cache capacity.
{% else %}
// Quantize new BSH K/V into an INT8 or packed INT4 BNSH cache.
{% endif %}
const HEAD_DIM: u32 = {{ headDim }}u;
{% if mode != "copy" %}const KV_HEADS: u32 = {{ kvHeads }}u;
{% endif %}
const WG: u32 = {{ tunables.COPY_WORKGROUP_SIZE }}u;
{% if mode != "copy" and (mode != "merge_share" or shareAppend) and not shiftRetainOnly %}const KV_HIDDEN: u32 = {{ kvHeads }}u * {{ headDim }}u;
{% endif %}
{% if mode == "build_quant" or mode == "append_quant" %}const PACKED: u32 = {{ packed }}u;
{% endif %}
{% if hasRotary and mode != "copy" and (mode != "merge_share" or shareAppend) %}const HALF: u32 = {{ half }}u;
{% endif %}
{% if hasKNorm and mode != "copy" and (mode != "merge_share" or shareAppend) %}const QK_EPS: f32 = {{ qkEps }};
{% endif %}
{% if mode == "build_quant" or mode == "append_quant" %}
const QMAX: f32 = {{ qmax }};
const QMIN: f32 = {{ qmin }};
fn kscale(d: u32, hk: u32) -> f32 { return k_scale[select(0u, hk * HEAD_DIM + d, params.perChannel != 0u)]; }
fn vscale(d: u32, hk: u32) -> f32 { return v_scale[select(0u, hk * HEAD_DIM + d, params.perChannel != 0u)]; }
{% endif %}

@compute @workgroup_size(WG)
fn main({% if needsGid %}@builtin(global_invocation_id) gid: vec3<u32>{% if cooperativeMode %},
        {% endif %}{% endif %}{% if cooperativeMode %}@builtin(workgroup_id) wid: vec3<u32>,
        @builtin(local_invocation_id) lid: vec3<u32>{% endif %}) {
{% macro append_cooperative_walk() %}
  // Compact cooperative append walk: the thread range spans only the appended
  // window (batch x kvHead x keySeq rows), not the full cache capacity; the
  // destination row is the dynamic append offset plus the local row.
  // The loop is bounded by the elements this workgroup owns rather than a fixed
  // HEAD_DIM trip count.
  let wgEnd = min(elemBase + WG * HEAD_DIM, totalElems);
  for (var e = elemBase + lid.x; e < wgEnd; e = e + WG) {
    {
      let d = e % HEAD_DIM;
      let et = e / HEAD_DIM;
      let j = et % params.keySeq;
      let etmp = et / params.keySeq;
      let hk = etmp % KV_HEADS;
      let b = etmp / KV_HEADS;
      // Clamping below by keySeq maps a right-padded first prompt
      // (seqlens_k[b]+1 < keySeq) to append offset 0.
      let activeEnd = min(params.seq, max(params.keySeq, u32(seqlens_k[b]) + 1u));
      let t = activeEnd - params.keySeq + j;
      let dst = ((b * KV_HEADS + hk) * params.seq + t) * HEAD_DIM + d;
      let nSrc = (b * params.keySeq + j) * KV_HIDDEN + hk * HEAD_DIM;
{% if hasRotary %}
      // Element-wise NeoX rotation: the pair (dr, dr+HALF) shares one
      // cos/sin entry, and row t is its own absolute position.
      let dr = select(d - HALF, d, d < HALF);
      let cs = cos_cache[t * HALF + dr];
      let sn = sin_cache[t * HALF + dr];
      let x0 = new_k[nSrc + dr];
      let x1 = new_k[nSrc + dr + HALF];
      present_key[dst] = select(x1 * cs + x0 * sn, x0 * cs - x1 * sn, d < HALF);
{% else %}
      present_key[dst] = new_k[nSrc + d];
{% endif %}
      present_value[dst] = new_v[nSrc + d];
    }
  }
{% endmacro %}
{% macro append_per_row_walk() %}
  // Per-row append walk: one thread streams its row's contiguous bytes.
{{ flat_index_2d("WG", guardInline=true) }}
  let j = i % params.keySeq;
  let tmp = i / params.keySeq;
  let hk = tmp % KV_HEADS;
  let b = tmp / KV_HEADS;
  // Clamping below by keySeq maps a right-padded first prompt
  // (seqlens_k[b]+1 < keySeq) to append offset 0.
  let activeEnd = min(params.seq, max(params.keySeq, u32(seqlens_k[b]) + 1u));
  let t = activeEnd - params.keySeq + j;
  let dstBase = ((b * KV_HEADS + hk) * params.seq + t) * HEAD_DIM;
  let nSrc = (b * params.keySeq + j) * KV_HIDDEN + hk * HEAD_DIM;
{% if hasRotary %}
  var k: array<f32, HEAD_DIM>;
  for (var d = 0u; d < HEAD_DIM; d = d + 1u) { k[d] = f32(new_k[nSrc + d]); }
  // Row t is its own absolute position in the shared cache.
  for (var d = 0u; d < HALF; d = d + 1u) {
    let cs = cos_cache[t * HALF + d];
    let sn = sin_cache[t * HALF + d];
    let x0 = k[d];
    let x1 = k[d + HALF];
    k[d] = x0 * cs - x1 * sn;
    k[d + HALF] = x1 * cs + x0 * sn;
  }
  for (var d = 0u; d < HEAD_DIM; d = d + 1u) {
    present_key[dstBase + d] = k[d];
    present_value[dstBase + d] = new_v[nSrc + d];
  }
{% else %}
  for (var d = 0u; d < HEAD_DIM; d = d + 1u) {
    present_key[dstBase + d] = new_k[nSrc + d];
    present_value[dstBase + d] = new_v[nSrc + d];
  }
{% endif %}
{% endmacro %}
{% if cooperativeMerge and (mode == "copy" or mode == "merge" or mode == "merge_share") %}
  // Each workgroup copies the contiguous element span of its WG rows
  // cooperatively: at step s lane l touches element s*WG + l, so adjacent
  // lanes hit adjacent addresses on both source and destination. Same
  // dispatch geometry (ceil(rows/WG) workgroups, folded into x/y).
  let wgFlat = wid.x + wid.y * {{ DISPATCH_FOLD_WIDTH }}u;
  let elemBase = wgFlat * (WG * HEAD_DIM);
  let totalElems = params.count * HEAD_DIM;
{% endif %}
{% if mode == "copy" and cooperativeCopy %}
  // Copy mode is an identity copy over the whole BNSH range: dst index == src index.
  for (var s = 0u; s < HEAD_DIM; s = s + 1u) {
    let e = elemBase + s * WG + lid.x;
    if (e < totalElems) {
      present_key[e] = src_k[e];
      present_value[e] = src_v[e];
    }
  }
{% elif mode == "merge" and cooperativeCopy %}
  // present[0:pastSeq] = past (BNSH copy); present[pastSeq:totalSeq] = new K/V (BSH appended).
  for (var s = 0u; s < HEAD_DIM; s = s + 1u) {
    let e = elemBase + s * WG + lid.x;
    if (e < totalElems) {
      let d = e % HEAD_DIM;
      let et = e / HEAD_DIM;
      let t = et % params.seq;
      let etmp = et / params.seq;
      let hk = etmp % KV_HEADS;
      let b = etmp / KV_HEADS;
      if (t < params.pastSeq) {
        let src = ((b * KV_HEADS + hk) * params.pastSeq + t) * HEAD_DIM + d;
        present_key[e] = past_k[src];
        present_value[e] = past_v[src];
      } else {
        let nSrc = (b * params.keySeq + (t - params.pastSeq)) * KV_HIDDEN + hk * HEAD_DIM + d;
        present_key[e] = new_k[nSrc];
        present_value[e] = new_v[nSrc];
      }
    }
  }
{% elif mode == "merge_share" and cooperativeMerge %}
{% if shareAppend %}
{% if cooperativeCopy %}
{{ append_cooperative_walk() }}
{% else %}
  if (params.count < WG) {
{{ append_cooperative_walk() }}
    return;
  }
{{ append_per_row_walk() }}
{% endif %}
{% else %}
  // Cooperative element walk (see the copy branch); the same-stride layout
  // makes the outside-window rows an identity copy (dst index == src index).
  for (var s = 0u; s < HEAD_DIM; s = s + 1u) {
    let e = elemBase + s * WG + lid.x;
    if (e < totalElems) {
      let et = e / HEAD_DIM;
      let t = et % params.seq;
      let b = et / (params.seq * KV_HEADS);
      // Clamping below by keySeq maps a right-padded first prompt
      // (seqlens_k[b]+1 < keySeq) to append offset 0.
      let activeEnd = min(params.seq, max(params.keySeq, u32(seqlens_k[b]) + 1u));
      let appendStart = activeEnd - params.keySeq;
      // Everything outside the append window. The append pass owns the window itself,
      // and the shared full-capacity stride makes this an identity copy (dst == src).
      if (t < appendStart || t >= activeEnd) {
        present_key[e] = past_k[e];
        present_value[e] = past_v[e];
      }
    }
  }
{% endif %}
{% elif mode == "copy" %}
  // Thread i streams one contiguous (batch, kvHead, token) row.
{{ flat_index_2d("WG", guardInline=true) }}
  let base = i * HEAD_DIM;
  for (var d = 0u; d < HEAD_DIM; d = d + 1u) {
    present_key[base + d] = src_k[base + d];
    present_value[base + d] = src_v[base + d];
  }
{% elif mode == "merge" %}
  // Per-row merge walk.
{{ flat_index_2d("WG", guardInline=true) }}
  let t = i % params.seq;
  let tmp = i / params.seq;
  let hk = tmp % KV_HEADS;
  let b = tmp / KV_HEADS;
  // present[0:pastSeq] = past (BNSH copy); present[pastSeq:totalSeq] = new K/V (BSH appended).
  let dstBase = ((b * KV_HEADS + hk) * params.seq + t) * HEAD_DIM;
  if (t < params.pastSeq) {
    let srcBase = ((b * KV_HEADS + hk) * params.pastSeq + t) * HEAD_DIM;
    for (var d = 0u; d < HEAD_DIM; d = d + 1u) {
      present_key[dstBase + d] = past_k[srcBase + d];
      present_value[dstBase + d] = past_v[srcBase + d];
    }
  } else {
    let nSrc = (b * params.keySeq + (t - params.pastSeq)) * KV_HIDDEN + hk * HEAD_DIM;
    for (var d = 0u; d < HEAD_DIM; d = d + 1u) {
      present_key[dstBase + d] = new_k[nSrc + d];
      present_value[dstBase + d] = new_v[nSrc + d];
    }
  }
{% elif mode == "merge_share" %}
  // Past and present share the full-capacity stride, so outside-window rows
  // copy at the same index.
{{ flat_index_2d("WG", guardInline=true) }}
  let t = i % params.seq;
  let tmp = i / params.seq;
  let hk = tmp % KV_HEADS;
  let b = tmp / KV_HEADS;
  // Clamping below by keySeq maps a right-padded first prompt
  // (seqlens_k[b]+1 < keySeq) to append offset 0.
  let activeEnd = min(params.seq, max(params.keySeq, u32(seqlens_k[b]) + 1u));
  let appendStart = activeEnd - params.keySeq;
  let dstBase = ((b * KV_HEADS + hk) * params.seq + t) * HEAD_DIM;
  // Everything outside the append window. The append pass owns the window itself,
  // and the shared full-capacity stride makes this an identity copy (dst == src).
  if (t < appendStart || t >= activeEnd) {
    for (var d = 0u; d < HEAD_DIM; d = d + 1u) {
      present_key[dstBase + d] = past_k[dstBase + d];
      present_value[dstBase + d] = past_v[dstBase + d];
  }
  }
{% elif mode == "window_shift" %}
  // Keep the most recent min(total, capacity) tokens in contiguous cache rows.
  // Read past and write a distinct present buffer so compaction cannot race.
  // Rotary append uses the absolute token position; retained keys are already rotated.
{% if shiftRegion == "append" %}
  // Append-only pass: the thread range spans just the appended window (batch x
  // kvHead x keySeq rows), while `params.seq` stays the cache capacity. The shift
  // pass owns every other row and the two ranges are disjoint, so their order is
  // immaterial.
{{ flat_index_2d("WG", guardInline=true) }}
  let j = i % params.keySeq;
  let tmp = i / params.keySeq;
  let hk = tmp % KV_HEADS;
  let b = tmp / KV_HEADS;
  let absTotal = max(params.keySeq, u32(seqlens_k[b]) + 1u);
  let residentBefore = min(absTotal - params.keySeq, params.seq);
  // `max(0u, a + b - c)` does not clamp in u32: the subtraction wraps first, so a
  // step that evicts nothing reads back ~2^32 instead of 0. Compare before
  // subtracting.
  let filled = residentBefore + params.keySeq;
  let evicted = select(0u, filled - params.seq, filled > params.seq);
  let appendStart = residentBefore - evicted;
  let t = appendStart + j;
  let dstBase = ((b * KV_HEADS + hk) * params.seq + t) * HEAD_DIM;
  let nSrc = (b * params.keySeq + j) * KV_HIDDEN + hk * HEAD_DIM;
  // Row appendStart + j carries absolute position absTotal - keySeq + j: the cache
  // holds only the last L positions, so the row index is short of the absolute one
  // by the window origin. The reference rotates the same rows at
  // `appendStart + cacheOrigin`, which is the same number.
  let pos = absTotal - params.keySeq + j;
  var k: array<f32, HEAD_DIM>;
  for (var d = 0u; d < HEAD_DIM; d = d + 1u) { k[d] = new_k[nSrc + d]; }
  for (var d = 0u; d < HALF; d = d + 1u) {
    let cs = cos_cache[pos * HALF + d];
    let sn = sin_cache[pos * HALF + d];
    let x0 = k[d];
    let x1 = k[d + HALF];
    k[d] = x0 * cs - x1 * sn;
    k[d + HALF] = x1 * cs + x0 * sn;
  }
  for (var d = 0u; d < HEAD_DIM; d = d + 1u) {
    present_key[dstBase + d] = k[d];
    present_value[dstBase + d] = new_v[nSrc + d];
  }
{% else %}
{{ flat_index_2d("WG", guardInline=true) }}
  let t = i % params.seq;
  let tmp = i / params.seq;
  let hk = tmp % KV_HEADS;
  let b = tmp / KV_HEADS;
  let absTotal = max(params.keySeq, u32(seqlens_k[b]) + 1u);
  let residentBefore = min(absTotal - params.keySeq, params.seq);
  // `max(0u, a + b - c)` does not clamp in u32: the subtraction wraps first, so a
  // step that evicts nothing reads back ~2^32 instead of 0. Compare before
  // subtracting.
  let filled = residentBefore + params.keySeq;
  let evicted = select(0u, filled - params.seq, filled > params.seq);
  let appendStart = residentBefore - evicted;
  let dstBase = ((b * KV_HEADS + hk) * params.seq + t) * HEAD_DIM;
  if (t < appendStart) {
    // Surviving past rows slide down by the eviction count.
    let srcBase = ((b * KV_HEADS + hk) * params.seq + (t + evicted)) * HEAD_DIM;
    for (var d = 0u; d < HEAD_DIM; d = d + 1u) {
      present_key[dstBase + d] = past_k[srcBase + d];
      present_value[dstBase + d] = past_v[srcBase + d];
    }
{% if shiftRegion == "shift" %}
  } else if (t >= appendStart + params.keySeq) {
{% else %}
  } else if (t < appendStart + params.keySeq) {
    let nSrc = (b * params.keySeq + (t - appendStart)) * KV_HIDDEN + hk * HEAD_DIM;
    for (var d = 0u; d < HEAD_DIM; d = d + 1u) {
      present_key[dstBase + d] = new_k[nSrc + d];
      present_value[dstBase + d] = new_v[nSrc + d];
    }
  } else {
{% endif %}
    // Outside the resident window. Cleared rather than left stale so the present
    // buffer does not expose stale contents from its distinct allocation.
    for (var d = 0u; d < HEAD_DIM; d = d + 1u) {
      present_key[dstBase + d] = {{ zeroScalar }}(0.0);
      present_value[dstBase + d] = {{ zeroScalar }}(0.0);
    }
  }
{% endif %}
{% else %}
{{ flat_index_2d("WG", guardInline=true) }}
  let t = i % params.seq;
  let tmp = i / params.seq;
  let hk = tmp % KV_HEADS;
  let b = tmp / KV_HEADS;
  let srcBase = (b * params.seq + t) * KV_HIDDEN + hk * HEAD_DIM; // BSH new K/V
  var k: array<f32, HEAD_DIM>;
  for (var d = 0u; d < HEAD_DIM; d = d + 1u) { k[d] = src_k[srcBase + d]; }
{% if hasKNorm %}
  var ms = 0.0;
  for (var d = 0u; d < HEAD_DIM; d = d + 1u) { ms = ms + k[d] * k[d]; }
  let invRms = inverseSqrt(ms / f32(HEAD_DIM) + QK_EPS);
  for (var d = 0u; d < HEAD_DIM; d = d + 1u) { k[d] = k[d] * invRms * k_norm_weight[d]; }
{% endif %}
{% if hasRotary %}
  let pos = params.pastSeq + t;
  for (var d = 0u; d < HALF; d = d + 1u) {
    let cs = cos_cache[pos * HALF + d];
    let sn = sin_cache[pos * HALF + d];
    let x0 = k[d];
    let x1 = k[d + HALF];
    k[d] = x0 * cs - x1 * sn;
    k[d + HALF] = x1 * cs + x0 * sn;
  }
{% endif %}
{% if mode == "build" %}
  let dstBase = ((b * KV_HEADS + hk) * params.seq + t) * HEAD_DIM;
  for (var d = 0u; d < HEAD_DIM; d = d + 1u) {
    present_key[dstBase + d] = k[d];
    present_value[dstBase + d] = src_v[srcBase + d];
  }
{% else %}
{% if mode == "append_quant" %}
  let activeEnd = u32(seqlens_k[b]) + 1u;
  let appendStart = activeEnd - params.seq;
  let dstBase = ((b * KV_HEADS + hk) * params.totalSeq + appendStart + t) * PACKED;
{% else %}
  let dstBase = ((b * KV_HEADS + hk) * params.seq + t) * PACKED;
{% endif %}
{% if bits == 8 %}
  for (var d = 0u; d < HEAD_DIM; d = d + 1u) {
    present_key[dstBase + d] = i32(clamp(round(k[d] / kscale(d, hk)), QMIN, QMAX));
    present_value[dstBase + d] = i32(clamp(round(src_v[srcBase + d] / vscale(d, hk)), QMIN, QMAX));
  }
{% else %}
  for (var dd = 0u; dd < PACKED; dd = dd + 1u) {
    let d0 = dd * 2u;
    let d1 = dd * 2u + 1u;
    let qk0 = i32(clamp(round(k[d0] / kscale(d0, hk)), QMIN, QMAX));
    let qk1 = i32(clamp(round(k[d1] / kscale(d1, hk)), QMIN, QMAX));
    let qv0 = i32(clamp(round(src_v[srcBase + d0] / vscale(d0, hk)), QMIN, QMAX));
    let qv1 = i32(clamp(round(src_v[srcBase + d1] / vscale(d1, hk)), QMIN, QMAX));
    present_key[dstBase + dd] = (u32(qk0 + 8) & 0xFu) | ((u32(qk1 + 8) & 0xFu) << 4u);
    present_value[dstBase + dd] = (u32(qv0 + 8) & 0xFu) | ((u32(qv1 + 8) & 0xFu) << 4u);
  }
{% endif %}
{% endif %}
{% endif %}
}
{% endif %}