CUDA: faster float -> iq4_nl conversion (#73)

* iqk_mul_mat: better iq4_nl implementation on Zen4/AVX2

PP-512 performance for LLaMA-3.1-8B goes to 162.6 t/s up
from 133.2 t/s.

* Speed up float -> iq4_nl conversion on CUDA

---------

Co-authored-by: Iwan Kawrakow <iwan.kawrakow@gmail.com>

Author: 2 people

ggml/src/ggml-cuda/cpy.cu

@@ -225,16 +225,21 @@ static __device__ void cpy_blck_f32_q5_1(const char * cxi, char * cdsti) {
     memcpy(dsti->qh, &qh, sizeof(qh));
 }
 
-
-static __device__ __forceinline__ int best_index_int8(int n, const int8_t * val, float x) {
-    if (x <= val[0]) return 0;
-    if (x >= val[n-1]) return n-1;
-    int ml = 0, mu = n-1;
-    while (mu-ml > 1) {
-        int mav = (ml+mu)/2;
-        if (x < val[mav]) mu = mav; else ml = mav;
-    }
-    return x - val[mu-1] < val[mu] - x ? mu-1 : mu;
+static __device__ const int8_t iq4nl_index[241] = {
+     0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 16, 16,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
+     1, 17, 17,  2,  2,  2,  2,  2,  2,  2,  2,  2,  2,  2,  2,  2,  2,  2,  2,  2,  2, 18,  3,  3,  3,  3,  3,  3,  3,  3,  3,  3,
+     3,  3,  3,  3,  3,  3, 19,  4,  4,  4,  4,  4,  4,  4,  4,  4,  4,  4,  4,  4,  4, 20,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,
+     5,  5, 21, 21,  6,  6,  6,  6,  6,  6,  6,  6,  6,  6,  6, 22,  7,  7,  7,  7,  7,  7,  7,  7,  7,  7, 23, 23,  8,  8,  8,  8,
+     8,  8,  8,  8,  8,  8, 24,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9, 25, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 26, 26,
+    11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 27, 27, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 28, 13, 13, 13,
+    13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 29, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
+    14, 14, 14, 14, 30, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15
+};
+static __device__ __forceinline__ int best_index_iq4nl(const int8_t * values, float x) {
+    int ix = (int)x - values[0];
+    if (ix < 0 || ix >= 241) return ix < 0 ? 0 : 15;
+    ix = iq4nl_index[ix];
+    return ix < 16 ? ix : x - values[ix-16] < values[ix-15] - x ? ix-16 : ix-15;
 }
 
 static __device__ void cpy_blck_f32_iq4_nl(const char * cxi, char * cdsti) {
@@ -255,12 +260,14 @@ static __device__ void cpy_blck_f32_iq4_nl(const char * cxi, char * cdsti) {
     float d = vmax / kvalues_iq4nl[0];
     const float id = d ? 1.0f/d : 0.0f;
 
+    //dsti->d = d;
+
     float sumqx = 0, sumq2 = 0;
     for (int j = 0; j < QK4_NL/2; ++j) {
         const float x0 = xi[0        + j]*id;
         const float x1 = xi[QK4_NL/2 + j]*id;
-        const uint8_t xi0 = best_index_int8(16, kvalues_iq4nl, x0);
-        const uint8_t xi1 = best_index_int8(16, kvalues_iq4nl, x1);
+        const uint8_t xi0 = best_index_iq4nl(kvalues_iq4nl, x0);
+        const uint8_t xi1 = best_index_iq4nl(kvalues_iq4nl, x1);
         dsti->qs[j] = xi0 | (xi1 << 4);
         const float v0 = kvalues_iq4nl[xi0];
         const float v1 = kvalues_iq4nl[xi1];