[libre-riscv-dev] [Bug 134] New: implement carry-less multiply

bugzilla-daemon at libre-riscv.org bugzilla-daemon at libre-riscv.org
Wed Aug 21 15:07:46 BST 2019


            Bug ID: 134
           Summary: implement carry-less multiply
           Product: Libre Shakti M-Class
           Version: unspecified
          Hardware: Other
                OS: Linux
            Status: CONFIRMED
          Severity: enhancement
          Priority: ---
         Component: ALU (including IEEE754 16/32/64-bit FPU)
          Assignee: lkcl at lkcl.net
          Reporter: programmerjake at gmail.com
                CC: libre-riscv-dev at lists.libre-riscv.org
   NLnet milestone: ---

Carry-less multiply could be implemented relatively inexpensively, sharing HW
with the SIMD integer/mantissa multiplier. All that would be needed is to mask
out the carry signals in the multiplier, which shouldn't have too much of an
incremental cost since it'd be converting 2-input AND gates to 3-input.

carry-less multiply is commonly used for cryptography, CRC calculation (used
for networking and compression/decompression), and more.

x86's version of carry-less multiply

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