Re: [PATCH] Re: Bignum performance (was: Shrinking the C core)

[Emanuel Berg <incal@dataswamp.org>]

Gerd Möllmann wrote:

>> Sorry, but I do not know how to do it. Not familiar
>> with CL.
>> 
> Ok. I used the code from
> https://dataswamp.org/~incal/cl/fib.cl/fib.cl

Yikes, how did that happen, some slip involving symbolic
links ...

Here it is: 
  https://dataswamp.org/~incal/cl/bench/fib.cl

And timing is done with this:
  https://dataswamp.org/~incal/cl/bench/timing.cl

Note the ugly absolute path in fib.cl BTW, otherwise you get
the path not of the file but of SBCL or Slime, maybe. I think
one is supposed to use ASDF, but surely there must some easy
way to just load a file using a relative path to the
current file?

(load "~/public_html/cl/bench/timing.cl")

> is the declaration (unsigned-byte 53).
>
> The declaration means we are lying to the compiler because
> Z gets bigger than 53 bits eventually. And all bets are off
> because of the OPTIMIZE declaration. The result is that
> everything is done in fixnums on 64-bit machines.

A very impressive optimization indeed, and expressed in
a cryptic way.

> ; disassembly for FIB
> ; Size: 92 bytes. Origin: #x700530086C                        ; FIB
> ; 6C:       030080D2         MOVZ NL3, #0
> ; 70:       040080D2         MOVZ NL4, #0
> ; 74:       0E000014         B L3
> ; 78: L0:   410080D2         MOVZ NL1, #2
> ; 7C:       E20301AA         MOV NL2, NL1
> ; 80:       EB030CAA         MOV R1, R2
> ; 84:       651100D1         SUB NL5, R1, #4
> ; 88:       000080D2         MOVZ NL0, #0
> ; 8C:       05000014         B L2
> ; 90: L1:   2300028B         ADD NL3, NL1, NL2
> ; 94:       E20301AA         MOV NL2, NL1
> ; 98:       E10303AA         MOV NL1, NL3
> ; 9C:       00080091         ADD NL0, NL0, #2
> ; A0: L2:   1F0005EB         CMP NL0, NL5
> ; A4:       6BFFFF54         BLT L1
> ; A8:       84080091         ADD NL4, NL4, #2
> ; AC: L3:   9F000AEB         CMP NL4, R0
> ; B0:       4BFEFF54         BLT L0
> ; B4:       EA0303AA         MOV R0, NL3
> ; B8:       FB031AAA         MOV CSP, CFP
> ; BC:       5A7B40A9         LDP CFP, LR, [CFP]
> ; C0:       BF0300F1         CMP NULL, #0
> ; C4:       C0035FD6         RET
>
> Tada!

How do you see only fixnums are used?

Are we talking 1 word = 2 bytes = 16 bits here, s2c?

If so, the range of fixnums are -32 768 to 32 767 inclusive,
so those are hardly huge numbers.

-- 
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