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| From: | Paolo Bonzini |
| Subject: | Re: [Lightning] Subtract with borrow |
| Date: | Wed, 05 Aug 2009 01:10:35 +0200 |
| User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1b3pre) Gecko/20090513 Fedora/3.0-2.3.beta2.fc11 Lightning/1.0pre Thunderbird/3.0b2 |
On 08/04/2009 07:19 PM, Mike Spivey wrote:
The i386 implementation in GIT contains the definition for
subtract-with-carry:
#define jit_subxr_i(d, s1, s2) \
jit_opr_((d), (s1), (s2), SBBLrr((s1), (d)), SBBLrr((s2), (d)) )
Please forgive my not compiling a test, but doesn't this treat
subtraction as if it is commutative? Correct code for the case where
s1 != d but s2 = d will be embarrassingly bad, but (if I'm right about
the error) bad code is better than wrong code, always!
I think you're right... :-( (The code wouldn't be so bad, it just needs some push/pops). Paolo
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