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code/.venv/lib/python3.12/site-packages/bitstring/fp8.py

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+"""
+The 8-bit float formats used here are from a proposal supported by Graphcore, AMD and Qualcomm.
+See https://arxiv.org/abs/2206.02915
+
+"""
+
+import struct
+import zlib
+import array
+import bitarray
+from bitstring.luts import binary8_luts_compressed
+import math
+
+
+class Binary8Format:
+    """8-bit floating point formats based on draft IEEE binary8"""
+
+    def __init__(self, exp_bits: int, bias: int):
+        self.exp_bits = exp_bits
+        self.bias = bias
+        self.pos_clamp_value = 0b01111111
+        self.neg_clamp_value = 0b11111111
+
+    def __str__(self):
+        return f"Binary8Format(exp_bits={self.exp_bits}, bias={self.bias})"
+
+    def decompress_luts(self):
+        binary8_to_float_compressed, float16_to_binary8_compressed = binary8_luts_compressed[(self.exp_bits, self.bias)]
+        self.lut_float16_to_binary8 = zlib.decompress(float16_to_binary8_compressed)
+        dec = zlib.decompress(binary8_to_float_compressed)
+        self.lut_binary8_to_float = struct.unpack(f'<{len(dec) // 4}f', dec)
+
+    def create_luts(self):
+        self.lut_binary8_to_float = self.createLUT_for_binary8_to_float()
+        self.lut_float16_to_binary8 = self.createLUT_for_float16_to_binary8()
+
+    def float_to_int8(self, f: float) -> int:
+        """Given a Python float convert to the best float8 (expressed as an integer in 0-255 range)."""
+        # First convert the float to a float16, then a 16 bit uint
+        try:
+            b = struct.pack('>e', f)
+        except (OverflowError, struct.error):
+            # Return the largest representable positive or negative value
+            return self.pos_clamp_value if f > 0 else self.neg_clamp_value
+        f16_int = int.from_bytes(b, byteorder='big')
+        # Then use this as an index to our large LUT
+        return self.lut_float16_to_binary8[f16_int]
+
+    def createLUT_for_float16_to_binary8(self) -> bytes:
+        # Used to create the LUT that was compressed and stored for the fp8 code
+        import gfloat
+        fi = gfloat.formats.format_info_p3109(8 - self.exp_bits)
+        fp16_to_fp8 = bytearray(1 << 16)
+        for i in range(1 << 16):
+            b = struct.pack('>H', i)
+            f, = struct.unpack('>e', b)
+            fp = gfloat.round_float(fi, f)
+            if math.isnan(fp):
+                fp8_i = 0b10000000
+            else:
+                fp8_i = self.lut_binary8_to_float.index(fp)
+            fp16_to_fp8[i] = fp8_i
+        return bytes(fp16_to_fp8)
+
+    def createLUT_for_binary8_to_float(self):
+        """Create a LUT to convert an int in range 0-255 representing a float8 into a Python float"""
+        i2f = []
+        for i in range(256):
+            b = bitarray.util.int2ba(i, length=8, endian='big', signed=False)
+            sign = b[0]
+            exponent = bitarray.util.ba2int(b[1:1 + self.exp_bits])
+            significand = b[1 + self.exp_bits:]
+            if exponent == 0:
+                significand = bitarray.bitarray('0') + significand
+                exponent = -self.bias + 1
+            else:
+                significand = bitarray.bitarray('1') + significand
+                exponent -= self.bias
+            f = float(bitarray.util.ba2int(significand)) / (2.0 ** (7 - self.exp_bits))
+            f *= 2 ** exponent
+            i2f.append(f if not sign else -f)
+        # One special case for minus zero
+        i2f[0b10000000] = float('nan')
+        # and for plus and minus infinity
+        i2f[0b01111111] = float('inf')
+        i2f[0b11111111] = float('-inf')
+        return array.array('f', i2f)
+
+
+# We create the 1.5.2 and 1.4.3 formats.
+p4binary_fmt = Binary8Format(exp_bits=4, bias=8)
+p3binary_fmt = Binary8Format(exp_bits=5, bias=16)
+
+
+def decompress_luts():
+    p4binary_fmt.decompress_luts()
+    p3binary_fmt.decompress_luts()