Re: a question abou "atoi"
William Pursell said:
On 31 Oct, 02:05, user923005 <dcor...@xxxxxxxxx> wrote:
for (index = 0; index < strlen(string); index++) {
substring[0] = string[index];
a = atoi(substring);
printf("%d\n", a);
}
Don't put strlen as a loop condition. Try:
len = strlen( string );
for( i = 0 ; i < len; i++ )
...
Probably best to explain why. Even though a skilled implementor of the
strlen function may well be able to use some clever tricks to speed it up
on a particular platform, its execution time is nevertheless going to be
approximately proportional to the length of the string, even for fairly
short strings, and *at the point of the call* a compiler will typically be
unable to prove that the string is not modified inside the loop, so it
won't be justified in caching the value. Thus, it will be called on every
single iteration of the loop, leading to O(n*n) behaviour - quadratic
performance, i.e. fairly dire. But *you* know the string is not modified
inside the loop, so you *are* justified in caching the value - and should
do so, as it reduces quadratic to linear.
--
Richard Heathfield <
http://www.cpax.org.uk>
Email: -
http://www. +rjh@
Google users: <
http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999
.
Relevant Pages
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... It is used to set upper loop -- limits for non-deterministic values thus avoiding the use of access -- types and enabling the functions to be used for synthesizeable code. ... DivisorVal: integer) return std_logic_vector; function "/"(DividendVal: string; DivisorVal: integer) return std_logic_vector; ... for loopVar in 0 to slvVal'length/4-1 loop ... end loop; if then return not resultVar; -- "width mismatch" errors here are due to improper sizing of the vector that this function is assigned to else return resultVar; -- "width mismatch" errors here are due to improper sizing of the vector that this function is assigned to end if; ...
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(comp.lang.vhdl) - extension_pack
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(comp.lang.vhdl) - extension_pack
... It is used to set upper loop -- limits for non-deterministic values thus avoiding the use of access -- types and enabling the functions to be used for synthesizeable code. ... DivisorVal: integer) return std_logic_vector; function "/"(DividendVal: string; DivisorVal: integer) return std_logic_vector; ... for loopVar in 0 to slvVal'length/4-1 loop ... end loop; if then return not resultVar; -- "width mismatch" errors here are due to improper sizing of the vector that this function is assigned to else return resultVar; -- "width mismatch" errors here are due to improper sizing of the vector that this function is assigned to end if; ...
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... The MAXIMUM size of a working string, accessed in its entirety, is ... compiler would generate a loop), ... > natural incompetence in the field of programming. ...
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