Fixing quantization int8 packing bug for NF4 and FP4

Author: Mhmd-Hisham

csrc/kernels.cu

@@ -431,7 +431,6 @@ __global__ void kQuantizeBlockwise(
             LoadFloat(loadf).Load(&rand[local_rand_idx], rand_vals, BLOCK_SIZE, 0);
         }
 
-        unsigned char packed_4bit = 0;
         switch (DATA_TYPE) {
         case General8bit:
 #pragma unroll NUM_PER_TH
@@ -445,17 +444,15 @@ __global__ void kQuantizeBlockwise(
         case FP4:
 #pragma unroll NUM_PER_TH
             for (int j = 0; j < NUM_PER_TH / 2; j++) {
-                packed_4bit |= dQuantizeFP4(((float)vals[2 * j]) * local_abs_max) << 4;
-                packed_4bit |= dQuantizeFP4(((float)vals[2 * j + 1]) * local_abs_max);
-                qvals[j] = packed_4bit;
+                qvals[j] = dQuantizeFP4(((float)vals[2 * j]) * local_abs_max) << 4;
+                qvals[j] |= dQuantizeFP4(((float)vals[2 * j + 1]) * local_abs_max);
             }
             break;
         case NF4:
 #pragma unroll NUM_PER_TH
             for (int j = 0; j < NUM_PER_TH / 2; j++) {
-                packed_4bit |= dQuantizeNF4(((float)vals[2 * j]) * local_abs_max) << 4;
-                packed_4bit |= dQuantizeNF4(((float)vals[2 * j + 1]) * local_abs_max);
-                qvals[j] = packed_4bit;
+                qvals[j] = dQuantizeNF4(((float)vals[2 * j]) * local_abs_max) << 4;
+                qvals[j] |= dQuantizeNF4(((float)vals[2 * j + 1]) * local_abs_max);
             }
             break;
         }

tests/test_functional.py

@@ -1125,21 +1125,20 @@ def test_4bit_quant(self, device, dtype, quant_type, blocksize):
 
         # With larger block sizes, we can expect this to blow up.
         # At blocksize>=1024, don't even bother looking at relerr.
-        if blocksize <= 64:
-            assert err.item() < 0.1
-            assert relerr.item() < 0.28
-        elif blocksize <= 256:
-            assert err.item() < 0.11
-            assert relerr.item() < 0.30
-        elif blocksize <= 512:
-            assert err.item() < 0.12
-            assert relerr.item() < 0.31
-        elif quant_type == "fp4":
-            # 1024 => 0.48, 2048 => 0.52, 4096 => 0.56
-            assert err.item() < 0.08 + math.log2(blocksize) * 4e-2
-        else:
-            # 1024 => 0.8, 2048 => 0.88, 4096 => 0.96
-            assert err.item() < math.log2(blocksize) * 8e-2
+        # 
+        # Actually, the above is not true anymore after fixing the integer packing bug.
+        # The following values were taken from averaging 1k samples per test configuration after fixing the bug.
+        error_dict = dict()
+        error_dict["fp4"] = dict()
+        error_dict["nf4"] = dict()
+        error_dict["fp4"]["err"] = {64: 0.096545, 128: 0.102947, 256: 0.108685, 512: 0.114087, 1024: 0.119312, 2048: 0.124460, 4096: 0.129573}
+        error_dict["fp4"]["rel_err"] = {64: 0.260130, 128: 0.275734, 256: 0.289842, 512: 0.302852, 1024: 0.314982, 2048: 0.326402, 4096: 0.337228}
+
+        error_dict["nf4"]["err"] = {64: 0.072792, 128: 0.076835, 256: 0.080326, 512: 0.083535, 1024: 0.086603, 2048: 0.089592, 4096: 0.092537}
+        error_dict["nf4"]["rel_err"] = {64: 0.203299, 128: 0.215252, 256: 0.226044, 512: 0.236021, 1024: 0.245365, 2048: 0.254146, 4096: 0.262457}
+
+        assert err < error_dict[quant_type]["err"][blocksize] + 1e-3
+        assert relerr < error_dict[quant_type]["rel_err"][blocksize] + 1e-3
 
     @pytest.mark.parametrize("device", get_available_devices())
     @pytest.mark.parametrize("quant_type", ["fp4", "nf4"])