[Misc] Disambiguate quantized types via a new ScalarType (#6396)

vllm/scalar_type.py

@@ -0,0 +1,35 @@
+from ._core_ext import NanRepr, ScalarType
+
+# naming generally follows: https://github.com/jax-ml/ml_dtypes
+# for floating point types (leading f) the scheme is:
+#  `float<size_bits>_e<exponent_bits>m<mantissa_bits>[flags]`
+#  flags:
+#  - no-flags: means it follows IEEE 754 conventions
+#  - f: means finite values only (no infinities)
+#  - n: means nans are supported (non-standard encoding)
+# for integer types the scheme is:
+#  `[u]int<size_bits>[b<bias>]`
+#  - if bias is not present it means its zero
+
+
+class scalar_types:
+    int4 = ScalarType.int_(4, None)
+    uint4 = ScalarType.uint(4, None)
+    int8 = ScalarType.int_(8, None)
+    uint8 = ScalarType.uint(8, None)
+    float8_e4m3fn = ScalarType.float_(4, 3, True,
+                                      NanRepr.EXTD_RANGE_MAX_MIN.value)
+    float8_e5m2 = ScalarType.float_IEEE754(5, 2)
+    float16_e8m7 = ScalarType.float_IEEE754(8, 7)
+    float16_e5m10 = ScalarType.float_IEEE754(5, 10)
+
+    # fp6, https://github.com/usyd-fsalab/fp6_llm/tree/main
+    float6_e3m2f = ScalarType.float_(3, 2, True, NanRepr.NONE.value)
+
+    # "gptq" types
+    uint4b8 = ScalarType.uint(4, 8)
+    uint8b128 = ScalarType.uint(8, 128)
+
+    # colloquial names
+    bfloat16 = float16_e8m7
+    float16 = float16_e5m10