Add 128 bit numbers

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kandamun

Joined: 20 Jul 2005
Posts: 25

kandamun 19 Feb 2008, 16:52

Hello all
Is there an instruction that adds two 128 bit numbers with carry?
I thought SSEx should have one but I could not find it.
And what is the most number of bits that can be ADDED with one instruction (with carry set)?

19 Feb 2008, 16:52

Borsuc

Joined: 29 Dec 2005
Posts: 2465
Location: Bucharest, Romania

Borsuc 19 Feb 2008, 16:57

kandamun wrote:

Hello all
Is there an instruction that adds two 128 bit numbers with carry?

You need two 64-bit adds, or four 32-bit adds, obviously to form a 128-bit add in both cases...

see Working with Big Numbers thread.

kandamun wrote:

And what is the most number of bits that can be ADDED with one instruction (with carry set)?

Infinite

as long as it fits in memory/RAM

19 Feb 2008, 16:57

kandamun

Joined: 20 Jul 2005
Posts: 25

kandamun 19 Feb 2008, 18:55

Thanks.
I know how to use 32-bit - add / adc .
But when there are 128 registers why isn't there 128 bit add instruction ?

19 Feb 2008, 18:55

r22

Joined: 27 Dec 2004
Posts: 805

r22 19 Feb 2008, 20:09

kandamun wrote:

Thanks.
I know how to use 32-bit - add / adc .
But when there are 128 registers why isn't there 128 bit add instruction ?

The 128bit registers are part of SSE.
SSE stands for Streaming SIMD Extensions.
SIMD stands for Single Instruction Multiple Data.

19 Feb 2008, 20:09

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20627
Location: In your JS exploiting you and your system

revolution 20 Feb 2008, 02:32

kandamun wrote:

Thanks.
I know how to use 32-bit - add / adc .
But when there are 128 registers why isn't there 128 bit add instruction ?

The registers are split into smaller parts, 64/32/16/8 bits, there is no instruction (yet) to work with all 128 bits as a single number. The MD part of SIMD implies that there is not just one piece of data in the register.

20 Feb 2008, 02:32

daniel.lewis

Joined: 28 Jan 2008
Posts: 92

daniel.lewis 21 Feb 2008, 06:34

Hmm... I should research to see if anyone has concieved of a parallelize-able lexer.

21 Feb 2008, 06:34

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