The support for BMI1 instruction set extension is almost universal by now. The extension was introduced in AMD Jaguar and Intel Haswell, both launched in 2013 i.e. 12 years ago.
Instead of doing stuff like (word >> bit_offset) & self.mask, in C or C++ I usually write _bextr_u64, or when using modern C# Bmi1.X64.BitFieldExtract. Note however these intrinsics compile into 2 instructions not one, because the CPU instruction takes start/length arguments from lower/higher bytes of a single 16-bit number.
I am handling a lot of vectors of size 6 or less with integers of values lower than 500.000. I am packing individual vectors in a u128, which comes down to 6*19 + a 3 bit length field = 117 bits with 11 bit left to spare.
I chose u128 instead of an array of [u64;2] due to the boundary crossing issue that I saw would happen, which I could avoid using u128.
I am not very familiar with these specific bit manipulation instruction sets, so would you know if there is something similar that works on u128 instead of just u32/u64?
I suspect that this unaligned read apporach doesn't work for a bit length of 59, 61, 62 and 63.
In the case of 63, reading out value at offset 1, requires two reads as it need 1 bit from the first byte, then 56 bits from the next 7 bytes and finally 6 bits from the 9th byte. Nine bytes cannot be loaded in a single u64 load.
The support for BMI1 instruction set extension is almost universal by now. The extension was introduced in AMD Jaguar and Intel Haswell, both launched in 2013 i.e. 12 years ago.
Instead of doing stuff like (word >> bit_offset) & self.mask, in C or C++ I usually write _bextr_u64, or when using modern C# Bmi1.X64.BitFieldExtract. Note however these intrinsics compile into 2 instructions not one, because the CPU instruction takes start/length arguments from lower/higher bytes of a single 16-bit number.
I am handling a lot of vectors of size 6 or less with integers of values lower than 500.000. I am packing individual vectors in a u128, which comes down to 6*19 + a 3 bit length field = 117 bits with 11 bit left to spare.
I chose u128 instead of an array of [u64;2] due to the boundary crossing issue that I saw would happen, which I could avoid using u128.
I am not very familiar with these specific bit manipulation instruction sets, so would you know if there is something similar that works on u128 instead of just u32/u64?
I suspect that this unaligned read apporach doesn't work for a bit length of 59, 61, 62 and 63.
In the case of 63, reading out value at offset 1, requires two reads as it need 1 bit from the first byte, then 56 bits from the next 7 bytes and finally 6 bits from the 9th byte. Nine bytes cannot be loaded in a single u64 load.