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Mojo function

set_neg_zero

def set_neg_zero[dtype: DType, width: Int]() -> SIMD[dtype, width]

Returns the universal "not ready" sentinel pack.

The pack is the fp32 -0.0 bit pattern (0x80000000) tiled over every 4 bytes. This one pattern is DTYPE-INDEPENDENT, yet has_neg_zero[dtype] detects it as the sentinel for every supported transport dtype, because:

the readiness poll is ANY-lane (it spins while any lane is -0.0), and
IEEE floats put the sign bit at the element MSB, so 0x80 every 4 bytes lands on a sign bit for fp32 (all lanes) and for the odd lanes of 2-byte dtypes (bf16/fp16) -- at least one -0.0 lane under each interpretation.

Parameters:

dtype (DType): The transport float type (bfloat16, float16, or float32).
width (Int): The SIMD pack width. width * sizeof(dtype) must be a multiple of 4 bytes (true for every 128-bit pack used by the protocol).

Returns:

SIMD[dtype, width]: The sentinel pack reinterpreted as SIMD[dtype, width].