cnpy.h::npy_save: fix bug when nels = 0 and data = NULL #87
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When nels = 0, no bytes from `const T* data` are written to the npy file (line 219: fwrite(data,sizeof(T),nels,fp)). Therefore, the crc of the to-be-written data only needs to be computed for the numpy header, as done on line 171. It might be thought that `crc32(initial_crc, data_ptr, data_size)` would always return `initial_crc` if `data_size = 0`. This is true for every value of data_ptr *except* NULL. In this case crc32 returns 0, *independent* of initial_crc. The result of calling npz_save with a shape of total size 0 (i.e., the product of all elements in the shape) should not depend on whether `data` is a null pointer or not. Fix this bug by only updating the crc when nels != 0, independent of the value of `data`.
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Reference for crc32: https://refspecs.linuxbase.org/LSB_3.0.0/LSB-Core-generic/LSB-Core-generic/zlib-crc32-1.html. In the Description section, "initial checksum" refers to zero. See the source code (https://github.com/madler/zlib/blob/master/crc32.c#L626) |
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When nels = 0, no bytes from
const T* dataare written to the npyfile (line 219: fwrite(data,sizeof(T),nels,fp)).
Therefore, the crc of the to-be-written data only needs to be
computed for the numpy header, as done on line 171.
It might be thought that
crc32(initial_crc, data_ptr, data_size)would always return
initial_crcifdata_size = 0. This is truefor every value of data_ptr except NULL. In this case crc32
returns 0, independent of initial_crc.
The result of calling npz_save with a shape of total size 0
(i.e., the product of all elements in the shape) should not depend
on whether
datais a null pointer or not.Fix this bug by only updating the crc when nels != 0, independent
of the value of
data.