Re: [algogeeks] Re: switch vs if -- which is faster
I was asking you for some examples ..as i dont have any knowledge regarding this assembly code and how to study it . there was no intention of mine to challenge you or disregard you . On 11/22/10, Gene gene.ress...@gmail.com wrote: I'm not sure what you mean by support. If you mean examples, gcc uses several of the techniques I mentioned. Write some switch statements with different distributions of cases. Compile with -S, and inspect the assembly code. If you don't now how to do that, take the time to learn. If you mean justify the truth of what I wrote, it's observation while studying and teaching courses about compilers on and off for over 15 years and building some myself. BTW, u c I won't ansr mor ??s if wrds arnt spld out... On Nov 22, 12:28 am, LALIT SHARMA lks.ru...@gmail.com wrote: @dipankar Can u tell us , sumthng more in support of ur ans...?? On Mon, Nov 22, 2010 at 10:40 AM, DIPANKAR DUTTA dutta.dipanka...@gmail.com wrote: both are same .. because any good optimizing compiler generate same assembly code of them... On Mon, Nov 22, 2010 at 9:38 AM, Gene gene.ress...@gmail.com wrote: A good compiler will never generate a switch that is slower than an if...else chain. It will analyze the switch cases and pick one of several options for code generation. These may include cascaded conditional jumps (like if...else code), simple jump tables, segmented jump tables (cascaded jumps pick one of several jump tables because a single table would be too big), binary searches in a sorted table of case values, and perfect hash functions. These are the ones I've seen. There may be others. On Nov 21, 8:15 am, shiva shivanand.kadwad...@gmail.com wrote: As per my understanding it is compiler depending thing.. what i feel is switch need to evaluate the expression only once but if else if need to evaluate the expression more than once(what if expression stored in variable and then compare...) Does any one please comment difference in speed of switch and if depending on how it is implemented... I heard switch uses jump table for its operation. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- DIPANKAR DUTTA M-TECH,Computer Science Engg. EC Dept,IIT ROORKEE Uttarakhand , India – 247667 --- website:http://people.iitr.ernet.in/shp/09535009/Website/index.html ph no-09045809987 email:dipan...@iitr.ernet.in -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- Lalit Kishore Sharma IIIT Allahabad (Amethi Capmus) 5th Sem -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- Lalit Kishore Sharma IIIT Allahabad (Amethi Capmus) 5th Sem -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
[algogeeks] Re: switch vs if -- which is faster
As he told you it depends on the data runs to the condition. If for
exampe statistically there is more of 1's then 0 then the switch loop
is faster, because:
1.) case is isolated
2.) You can reorder the case-statement according to the occurrent of
the conditions
On Nov 21, 2:59 pm, shiva shivanand.kadwad...@gmail.com wrote:
how it going to make difference in following case
--
i=0;
switch(i)
{
case 1: //some operation
case 0:// some operation}
--
i=0;
if(i==1)
{
//some operation;}
else if (i==0)
{
//Some operation}
--
even compiler implement jump table like below
key address
1 x
0 y
Then two condition (worst case) need to be checked which is same as if
else if
Please correct me if i am wrong
On Nov 21, 6:35 pm, MOHIT mohit...@gmail.com wrote:
for switch in the worst case compiler will generate if else chain .. else it
uses binary decision tree or jump table for optimization at compile time .
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Re: [algogeeks] Re: switch vs if -- which is faster
its depend on compiler how it optimize it . he can make binary search tree
for this comparison
or perform cascading comparison as in if else case .. so worst case
complexity will be as of
if- else .
but for this case
switch(i)
{
case 4: //some operation
case 5:// some operation
case 6 : //
some operation
}
optimization can be done by compiler which need no comparison
just need to calculate index which need to comparison...
so in above case switch is better than if else.
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[algogeeks] Re: switch vs if -- which is faster
@Mohit:
No, it's just the hierarchical occurent of conditions that makes the
switch faster. I really doubt that a compiler build a binary search
tree for switches. Also, it a binary tree works for switches why it
can't optimize the if-else-condition? Did you make some testing?
On Nov 21, 3:28 pm, MOHIT mohit...@gmail.com wrote:
its depend on compiler how it optimize it . he can make binary search tree
for this comparison
or perform cascading comparison as in if else case .. so worst case
complexity will be as of
if- else .
but for this case
switch(i)
{
case 4: //some operation
case 5:// some operation
case 6 : //
some operation
}
optimization can be done by compiler which need no comparison
just need to calculate index which need to comparison...
so in above case switch is better than if else.
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[algogeeks] Re: switch vs if -- which is faster
A good compiler will never generate a switch that is slower than an if...else chain. They will analyze the switch cases and pick one of several options for code generation. These may include cascaded conditional jumps (like if...else code), simple jump tables, segmented jump tables (cascaded jumps pick one of several jump tables because a single table would be too big), binary searches in a sorted table of case values, and perfect hash functions. These are the ones I've seen. There may be others. On Nov 21, 8:15 am, shiva shivanand.kadwad...@gmail.com wrote: As per my understanding it is compiler depending thing.. what i feel is switch need to evaluate the expression only once but if else if need to evaluate the expression more than once(what if expression stored in variable and then compare...) Does any one please comment difference in speed of switch and if depending on how it is implemented... I heard switch uses jump table for its operation. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
Re: [algogeeks] Re: switch vs if -- which is faster
both are same .. because any good optimizing compiler generate same assembly code of them... On Mon, Nov 22, 2010 at 9:38 AM, Gene gene.ress...@gmail.com wrote: A good compiler will never generate a switch that is slower than an if...else chain. They will analyze the switch cases and pick one of several options for code generation. These may include cascaded conditional jumps (like if...else code), simple jump tables, segmented jump tables (cascaded jumps pick one of several jump tables because a single table would be too big), binary searches in a sorted table of case values, and perfect hash functions. These are the ones I've seen. There may be others. On Nov 21, 8:15 am, shiva shivanand.kadwad...@gmail.com wrote: As per my understanding it is compiler depending thing.. what i feel is switch need to evaluate the expression only once but if else if need to evaluate the expression more than once(what if expression stored in variable and then compare...) Does any one please comment difference in speed of switch and if depending on how it is implemented... I heard switch uses jump table for its operation. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.comalgogeeks%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- DIPANKAR DUTTA M-TECH,Computer Science Engg. EC Dept,IIT ROORKEE Uttarakhand , India – 247667 --- website:http://people.iitr.ernet.in/shp/09535009/Website/index.html ph no-09045809987 email:dipan...@iitr.ernet.in email%3adipan...@iitr.ernet.in -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
Re: [algogeeks] Re: switch vs if -- which is faster
@dipankar Can u tell us , sumthng more in support of ur ans...?? On Mon, Nov 22, 2010 at 10:40 AM, DIPANKAR DUTTA dutta.dipanka...@gmail.com wrote: both are same .. because any good optimizing compiler generate same assembly code of them... On Mon, Nov 22, 2010 at 9:38 AM, Gene gene.ress...@gmail.com wrote: A good compiler will never generate a switch that is slower than an if...else chain. They will analyze the switch cases and pick one of several options for code generation. These may include cascaded conditional jumps (like if...else code), simple jump tables, segmented jump tables (cascaded jumps pick one of several jump tables because a single table would be too big), binary searches in a sorted table of case values, and perfect hash functions. These are the ones I've seen. There may be others. On Nov 21, 8:15 am, shiva shivanand.kadwad...@gmail.com wrote: As per my understanding it is compiler depending thing.. what i feel is switch need to evaluate the expression only once but if else if need to evaluate the expression more than once(what if expression stored in variable and then compare...) Does any one please comment difference in speed of switch and if depending on how it is implemented... I heard switch uses jump table for its operation. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- DIPANKAR DUTTA M-TECH,Computer Science Engg. EC Dept,IIT ROORKEE Uttarakhand , India – 247667 --- website:http://people.iitr.ernet.in/shp/09535009/Website/index.html ph no-09045809987 email:dipan...@iitr.ernet.in -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- Lalit Kishore Sharma IIIT Allahabad (Amethi Capmus) 5th Sem -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
[algogeeks] Re: switch vs if -- which is faster
I'm not sure what you mean by support. If you mean examples, gcc uses several of the techniques I mentioned. Write some switch statements with different distributions of cases. Compile with -S, and inspect the assembly code. If you don't now how to do that, take the time to learn. If you mean justify the truth of what I wrote, it's observation while studying and teaching courses about compilers on and off for over 15 years and building some myself. BTW, u c I won't ansr mor ??s if wrds arnt spld out... On Nov 22, 12:28 am, LALIT SHARMA lks.ru...@gmail.com wrote: @dipankar Can u tell us , sumthng more in support of ur ans...?? On Mon, Nov 22, 2010 at 10:40 AM, DIPANKAR DUTTA dutta.dipanka...@gmail.com wrote: both are same .. because any good optimizing compiler generate same assembly code of them... On Mon, Nov 22, 2010 at 9:38 AM, Gene gene.ress...@gmail.com wrote: A good compiler will never generate a switch that is slower than an if...else chain. It will analyze the switch cases and pick one of several options for code generation. These may include cascaded conditional jumps (like if...else code), simple jump tables, segmented jump tables (cascaded jumps pick one of several jump tables because a single table would be too big), binary searches in a sorted table of case values, and perfect hash functions. These are the ones I've seen. There may be others. On Nov 21, 8:15 am, shiva shivanand.kadwad...@gmail.com wrote: As per my understanding it is compiler depending thing.. what i feel is switch need to evaluate the expression only once but if else if need to evaluate the expression more than once(what if expression stored in variable and then compare...) Does any one please comment difference in speed of switch and if depending on how it is implemented... I heard switch uses jump table for its operation. -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- DIPANKAR DUTTA M-TECH,Computer Science Engg. EC Dept,IIT ROORKEE Uttarakhand , India – 247667 --- website:http://people.iitr.ernet.in/shp/09535009/Website/index.html ph no-09045809987 email:dipan...@iitr.ernet.in -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en. -- Lalit Kishore Sharma IIIT Allahabad (Amethi Capmus) 5th Sem -- You received this message because you are subscribed to the Google Groups Algorithm Geeks group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
