3 ms·

Modulo by a constant doesn't require a division, you can instead use multiplications, shifts, adds and subtracts. This transform is typical for compilers. For

by caf 10y ago

Modulo by a constant doesn't require a division, you can instead use multiplications, shifts, adds and subtracts. This transform is typical for compilers. For example, this is what gcc targetting x86_64 does to perform % 17 on the unsigned value in %edi: movl $-252645135, %edx movl %edi, %eax mull %edx movl %edx, %eax shrl $4, %eax movl %eax, %edx sall $4, %edx addl %edx, %eax subl %eax, %edi

lorenzhs 10y ago
That only works for compile time constants, though. With a power of two sized buffer you can just store the mask and decide how large you want your buffer to be at runtime.
- _ihaque 10y ago
  libdivide (http://libdivide.com http://libdivide.com) implements similar logic at runtime
- nullc 10y ago
  You can also compute the optimization at runtime, same as the compiler does. Libtheora contains code for this, used for quantizing video data.
userbinator 10y ago
It doesn't require division, but how is that long sequence of instructions going to beat an AND?