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urgent fix: exclusive scan computing pointers list #68

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Merged
thomasw21 merged 1 commit into from
Aug 18, 2021
Merged

urgent fix: exclusive scan computing pointers list #68

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20 changes: 7 additions & 13 deletions megatron/data/indexed_dataset.py
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Original file line number Diff line number Diff line change
Expand Up @@ -359,22 +359,16 @@ def _get_pointers(sizes, npdtype):
"""Return a numpy array of byte offsets given a list of sizes.

Multiplies values in the sizes array by dtype size (bytes),
and then computes a zero-based prefix scan.
and then computes an exclusive scan to get byte offsets.
"""

# create numpy array of desired numpy datatype
pointers = np.array(sizes, dtype=npdtype)
# compute element sizes in bytes
bytesizes = np.array(sizes, dtype=npdtype)
bytesizes *= dtype().itemsize

if len(sizes) > 0:
# scale each element by its dtype size
dtype_size = dtype().itemsize
pointers *= dtype_size

# in-place prefix scan to compute byte offsets
np.cumsum(pointers, axis=0, out=pointers)

# zero-base the prefix scan (exclusive scan)
pointers -= pointers[0]
# exclusive scan to get byte offsets
pointers = np.cumsum(bytesizes, axis=0)
pointers -= bytesizes

return pointers

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