Zakir032002 commented on PR #3329:
URL: https://github.com/apache/fory/pull/3329#issuecomment-3950638059
hey @asadjan4611, went through `bfloat16.pyx` — two bugs here
**NaN becomes Infinity**
for a signaling NaN like `0x7F800001`:
```
bf16_bits = 0x7F800001 >> 16 → 0x7F80
truncated = 0x7F800001 & 0xFFFF → 0x0001
0x0001 > 0x8000 → false, no rounding fires
returns 0x7F80 → Infinity, not NaN
```
fix — add NaN passthrough at the top (also note: `cdef` inside `if` block is
illegal in Cython, all declarations go at function top):
```cython
cdef inline uint16_t float32_to_bfloat16_bits(float value) nogil:
cdef uint32_t f32_bits
cdef uint16_t bf16_bits
cdef uint16_t truncated
memcpy(&f32_bits, &value, 4)
if (f32_bits & 0x7FFFFFFF) > 0x7F800000:
return (<uint16_t>(f32_bits >> 16)) | 0x0040
bf16_bits = <uint16_t>(f32_bits >> 16)
truncated = <uint16_t>(f32_bits & 0xFFFF)
if truncated > 0x8000:
bf16_bits += 1
elif truncated == 0x8000 and (bf16_bits & 1):
bf16_bits += 1
return bf16_bits
```
**`__hash__` breaks the eq contract for ±0**
`__eq__` returns `True` for `+0 == -0` but `hash(0x0000) != hash(0x8000)` —
python requires equal objects to have equal hashes, so `{bfloat16(0.0),
bfloat16(-0.0)}` silently gives 2 elements instead of 1.
```cython
def __hash__(self):
if (self._bits & 0x7FFF) == 0:
return hash(0)
return hash(self._bits)
```
Happy to discuss if im misreading the flow here
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