Optimise non-native 128-bit addition in int128.h. On platforms without native 128-bit integer support, simplify the test for carry in int128_add_uint64() by noting that the low-part addition is unsigned integer arithmetic, which is just modular arithmetic. Therefore the test for carry can simply be written as "new value < old value" (i.e., a test for modular wrap-around). This can then be made branchless so that on modern compilers it produces the same machine instructions as native 128-bit addition, making it significantly simpler and faster.
Similarly, the test for carry in int128_add_int64() can be written in much the same way, but with an extra term to compensate for the sign of the value being added. Again, on modern compilers this leads to branchless code, often identical to the native 128-bit integer addition machine code. Author: Dean Rasheed <dean.a.rash...@gmail.com> Reviewed-by: John Naylor <johncnaylo...@gmail.com> Discussion: https://postgr.es/m/caezatcwgbmc9zwkmyqqpaqz2x6gaamyrb+rnmsuncdmcl2m...@mail.gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/d9bb8ef093d62763cfd19d37e6bb8182998a3f88 Modified Files -------------- src/include/common/int128.h | 36 ++++++++++++++++-------------------- 1 file changed, 16 insertions(+), 20 deletions(-)
