Re: ASM for math

[A complimentary Cc of this posting was sent to
John W Kennedy
<jwkenne@xxxxxxxxxxxxx>], who wrote in article <48dbfb58$0$4917$607ed4bc@xxxxxx>:
express. Most processors have special tricks for multi-word arithmetic
(such as the Intel ADC instruction or the new z/Architecture ALC family
of instructions) that cannot be expressed at all in, say, C. (That is, C
has no way of saying, "Add X to Y, and add an additional 1 if the last
addition set the CPU carry flag.")

IIRC, PARI does not use anything "as advanced as that" ;-). There are
about 10 macros which an architecture should better imlement in
assembler; they are all very primitive, like

add two numbers and return the carry flag,
word x word --> twowords multiplication,
calculate number of trailing 0bits in a word, etc.

A typical PARI assembler file for an architecture is about 100 LOC.
(GMP kernel uses much larger assembler base, so it may be slightly
quickier for very large numbers - and slower for smaller ones for
independent reasons.)

Hope this helps,
Ilya
.

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