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Re: [Lightning] Reducing opcode permutations


From: Sandro Magi
Subject: Re: [Lightning] Reducing opcode permutations
Date: Fri, 28 Mar 2008 12:37:41 -0400

On Fri, Mar 28, 2008 at 12:20 PM, Paolo Bonzini <address@hidden> wrote:
>
>  > jit_movi_i(JIT_R1, INT_MAX)     // R1 = 2^31
>  > jit_addci_i(JIT_R0, JIT_R1, 1)   // R0 = R1 + 1, set carry
>  > jit_addxi_i(JIT_R2, JIT_R0, 0)   // R2 = R0 + 0 + carry
>
>  Don't confuse carry with overflow.  Carry is the same for integer and
>  unsigned integer.  Overflow differs, but what tests overflow is
>  boadd/bosub, not addc/addx.

Ah, my mistake. So a similar instruction sequence to the above using
boadd_i would branch to the overflow address, but if I were to use
boadd_ui it would not?

Sandro




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