Simple examples using dynasm
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dynasm jit playground

Playing around with dynasm

Example 1.

examp1 is really basic, just to show how .dasc files look like

Example 2.

LIttle more complicated, it is implementation of CRC using Intel's Slicing-by-4 technique.

There are 3 implementations, one directly in C, and two others in dasm: x86 and x64 version.

I wouldn't call this example jit, it simply uses dasm instead of Visual's builtin asm (which won't work for x64, and you'd have to create separate asm files)

There are few caveats:

  • I've made precomputed CRC table 1D, to make access easiers from asm

  • I've dropped end part from crc calculation, so buffer size must be multiple of 4

  • it has 'relative local labels', there can be up to 10 labels numbered from 0-9

    • when using them, you need to specify whether you're jumping backward (<) or forward (>)
    • if you use them, you need to call dasm_setupglobal, in my case it's in ctor of DynAsm object
  • I'm not sure if it's bug or not, but dasm_put for both x86 and x64 uses va_arg(*, int), which totally screws up pointers in x64 (and probably any 64-bit values for that matter).

    • so in x64 version I had to pass pointer to crc table as another argument
  • I'a probably never found it out by myself, there's mov64 instruction, that does what I've needed, see here:

Example results from my laptop

jitdemo> bin\examp2_x86.exe
compiled for x86
jit returend value: 4281082894 time: 0.111525 spd: 896.658 Mb/s
c   returend value: 4281082894 time: 0.138894 spd: 719.976 Mb/s

jitdemo> bin\examp2_x64.exe
compiled for x64
jit returend value: 4281082894 time: 0.111745 spd: 894.891 Mb/s
c   returend value: 4281082894 time: 0.144186 spd: 693.548 Mb/s

Example 3.

Is implementation of counter machine and is much more complicated. You can find detailed description in

Some cool numbers while testing fibonacci:

compiled for x64
value in cell number 0: 165580141
 * no-jit  time: 1.70075

value in cell number 0: 165580141
 *    jit  time: 0.399607