Code Density Comparison of two unsigned 24-bit values: x64 vs ϕEngine

[PabloMack]

I just rewrote an assembly function for the Pelles C assembler that compares two unsigned 24-bit integers. The function returns 1 for greater, 0 for equal and -1 for less than. I thought some of you might find it interesting. The x64 version was 45 bytes in size. I wrote a ϕEngine version and it is 15 bytes, only 1/3 the size. But this should not be surprising since ϕEngine can process 3-byte integers natively. Here is the source code:

 ⅅCPU Eng32
ut_cmp‡: ⅅPBeg
    ld     ⓊQ0,ut:(Ⓡ0)
    cmp    ⓊQ0,ut:(Ⓡ1)
    s.A*   Ⓒ0,ⓊQ0
    s.B*   Ⓒ0,ⓈQ0
    rts
 ⅅPEnd

Notice that the processing has to be done in a 32-bit register (ⓊQ0) which also is used to hold the return value. The two source values are extended during the loads so there are no separate conversion routines. The second load is part of the compare instruction. Most of the code is for producing a return value from the flags that are set by the compare. Since this operation can be done inline cheaper than even just the setup for function call, the function would actually never be needed in ϕPPL or ϕAsm.