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metal : optimize dequant q6_K kernel #11892

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Feb 15, 2025
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metal : optimize dequant q6_K kernel #11892

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33 changes: 21 additions & 12 deletions ggml/src/ggml-metal/ggml-metal.metal
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Original file line number Diff line number Diff line change
Expand Up @@ -373,24 +373,33 @@ void dequantize_q5_K(device const block_q5_K *xb, short il, thread type4x4 & reg
template <typename type4x4>
void dequantize_q6_K(device const block_q6_K *xb, short il, thread type4x4 & reg) {
const half d_all = xb->d;
device const uint8_t * ql = (device const uint8_t *)xb->ql;
device const uint8_t * qh = (device const uint8_t *)xb->qh;
device const uint16_t * ql = (device const uint16_t *)xb->ql;
device const uint16_t * qh = (device const uint16_t *)xb->qh;
device const int8_t * scales = (device const int8_t *)xb->scales;

ql = ql + 64*(il/8) + 32*((il/2)&1) + 16*(il&1);
qh = qh + 32*(il/8) + 16*(il&1);
ql = ql + 32*(il/8) + 16*((il/2)&1) + 8*(il&1);
qh = qh + 16*(il/8) + 8*(il&1);
float sc = scales[(il%2) + 2 * ((il/2))];
il = (il/2) & 3;

const uint16_t kmask1 = il>1 ? (il>2 ? 192 : 48) : (il>0 ? 12 : 3);
const uint16_t kmask2 = il>1 ? 0xF0 : 0x0F;
const float coef = il>1 ? 1.f/16.f : 1.f;
const uint32_t kmask1 = il>1 ? (il>2 ? 0xC0C0C0C0 : 0x30303030) : (il>0 ? 0x0C0C0C0C : 0x03030303);
const uint32_t kmask2 = il>1 ? 0xF0F0F0F0 : 0x0F0F0F0F;
const float ml = d_all * sc * 32.f;
const float dl = d_all * sc * coef;
for (int i = 0; i < 16; ++i) {
const half q = il&1 ? ((ql[i] & kmask2) | ((qh[i] & kmask1) << 2))
: ((ql[i] & kmask2) | ((qh[i] & kmask1) << 4));
reg[i/4][i%4] = dl * q - ml;
const float dl0 = d_all * sc;
const float dl1 = dl0 / 256.f;
const float dl2 = dl0 / (256.f * 256.f);
const float dl3 = dl0 / (256.f * 256.f * 256.f);
const uint8_t shr_h = il>2 ? 2 : 0;
const uint8_t shl_h = il>1 ? 0 : (il>0 ? 2 : 4);
const uint8_t shr_l = il>1 ? 4 : 0;
for (int i = 0; i < 4; ++i) {
const uint32_t low = (ql[2*i] | (uint32_t)(ql[2*i+1] << 16)) & kmask2;
const uint32_t high = (qh[2*i] | (uint32_t)(qh[2*i+1] << 16)) & kmask1;
const uint32_t q = ((high << shl_h) >> shr_h) | (low >> shr_l);
reg[i][0] = dl0 * ((half)(q & 0xFF)) - ml;
reg[i][1] = dl1 * ((float)(q & 0xFF00)) - ml;
reg[i][2] = dl2 * ((float)(q & 0xFF0000)) - ml;
reg[i][3] = dl3 * ((float)(q & 0xFF000000)) - ml;
}
}

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