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fix: replace __uint128_t with portable 64-bit decomposition in c_shard_info.pyx (MSVC build failure) #950

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fix: replace __uint128_t with portable 64-bit decomposition in c_shard_info.pyx (MSVC build failure) #950

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15 changes: 11 additions & 4 deletions cassandra/c_shard_info.pyx
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Original file line number Diff line number Diff line change
Expand Up @@ -14,9 +14,6 @@

from libc.stdint cimport INT64_MIN, UINT32_MAX, uint64_t, int64_t

cdef extern from *:
ctypedef unsigned int __uint128_t

cdef class ShardingInfo():
cdef readonly int shards_count
cdef readonly unicode partitioner
Expand All @@ -39,5 +36,15 @@ cdef class ShardingInfo():
def shard_id_from_token(self, int64_t token_input):
cdef uint64_t biased_token = token_input + (<uint64_t>1 << 63);
biased_token <<= self.sharding_ignore_msb;
cdef int shardId = (<__uint128_t>biased_token * self.shards_count) >> 64;
# Compute (biased_token * shards_count) >> 64, i.e. the high 64 bits of the
# 64x32-bit product, using only 64-bit arithmetic. This used to rely on the
# GCC/Clang-only __uint128_t extension type, which MSVC does not support at
# all (no 128-bit integer type), causing a compile error on Windows builds.
# The split below is a standard, portable multiply-high decomposition and is
# numerically identical to the previous 128-bit computation.
cdef uint64_t shards_count = <uint64_t>self.shards_count
cdef uint64_t low_product = (biased_token & <uint64_t>UINT32_MAX) * shards_count
cdef uint64_t carry = low_product >> 32
cdef uint64_t mid = (biased_token >> 32) * shards_count + carry
cdef int shardId = <int>(mid >> 32);
return shardId
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