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The Answer Why There Is No Shalq In Gpu Instruction Set

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Orion_    1

I had a problem with negative value using some gpu code, and I came to the conclusion that one of my routine didn't work, actually this was the GT Turbo's routine (not surprised ? ^^)

we complained about the missing shalq instruction in gpu instruction set, we have sharq, but not shalq, so why ?

because we simply don't need it ...

let's see, here is the GT Turbo's routine for SHALQ:

MACRO    SHALQ    a,b    ; by GT_Turbo
    shlq    \a,\b
    jr    NC,.pasign\~
    neg    \b


what shalq does ? it will shift the register to left, so let's take 2 numbers:

(decimal) 25 -> (binary) 00000000000000000000000000011001

(decimal) -25 -> (binary) 11111111111111111111111111100111


if you shift both of the binary number of 1 to left, you have:

00000000000000000000000000110010 -> 50

11111111111111111111111111001110 -> -50


and this can be achieved using a simple shlq, that's why we don't need shalq :)

but we do need sharq, because if you shift using a simple shrq a zero will be introduced in bit 31 of the number and it will screw up the negative value.

so correct me If I'm wrong, but I replaced all the SHALQ of my routine by shlq and the bug was gone !

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SCPCD    0




I don't know why GT have made and used this function because this things as already said somewhere on jagware that a simple shlq is the same as shalq... :P


EDIT : Link

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GT Turbo    5

A little problem Orion, it's not mine, because i don't use macro, i think that come from Macronator (SebRmv) no ?


GT :)

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Orion_    1

SCPCD > oops sorry, I didn't looked the end of this topic, so this one is useless I'm sorry ^^



GT Turbo > yes that's me who converted it to macro ^^

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