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POSmallest method of turning a string into an integer(and vice-versa)
primarykey
Id
1972803
data
AcceptedAnswerId
1972833
AnswerCount
8
ClosedDate
CommentCount
8
CommunityOwnedDate
CreationDate
2009-12-29T03:47:16.690
FavoriteCount
3
LastActivityDate
2009-12-29T08:49:38.480
LastEditDate
2009-12-29T05:52:47.953
LastEditorUserId
69742
OwnerUserId
69742
ParentId
0
PostTypeId
1
Score
4
ViewCount
974
LastEditorDisplayName
text
Body
I am looking for an extremely small way of turning a string like <code>"123"</code> into an integer like <code>123</code> and vice-versa. I will be working in a freestanding environment. This is NOT a premature optimization. I am creating code that must fit in 512 bytes, so every byte does actually count. I will take both x86 assembly(16 bit) and C code though(as that is pretty easy to convert) It does not need to do any sanity checks or anything.. I thought I had seen a very small C implementation implemented recursively, but I can't seem to find anything for size optimization.. So can anyone find me(or create) a very small atoi/itoa implementation? (it only needs to work with base 10 though) Edit: (the answer) (edited again because the first code was actually wrong) in case someone else comes upon this, this is the code I ended up creating. It could fit in 21 bytes! <pre><code>;ds:bx is the input string. ax is the returned integer _strtoint: xor ax,ax .loop1: imul ax, 10 ;ax serves as our temp var mov cl,[bx] mov ch,0 add ax,cx sub ax,'0' inc bx cmp byte [bx],0 jnz .loop1 ret </code></pre> Ok, last edit I swear! Version weighing in at 42 bytes with negative number support.. so if anyone wants to use these they can.. <pre><code> ;ds:bx is the input string. ax is the returned integer _strtoint: cmp byte [bx],'-' je .negate ;rewrite to negate DX(just throw it away) mov byte [.rewrite+1],0xDA jmp .continue .negate: mov byte [.rewrite+1],0xD8 inc bx .continue xor ax,ax .loop1: imul ax, 10 ;ax serves as our temp var mov dl,[bx] mov dh,0 add ax,dx sub ax,'0' inc bx cmp byte [bx],0 jnz .loop1 ;popa .rewrite: neg ax ;this instruction gets rewritten to conditionally negate ax or dx ret </code> </pre>
Tags
<c><optimization><assembly>
Title
Smallest method of turning a string into an integer(and vice-versa)
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