I want to write something like
status_bit = (unsigned)(i - j) >> 31

as an equivalent code for
if(i < j){
{
status_bit = 1;
}else{
status_bit = 0;
}

This actually works for most of the cases but fails for two values
i = 0x80000000
j = 0x7fffffff

I want a linear code for the above i.e. without jumps, so
1. what could be the issue?
2. what could be the solution?

On Oct 21, 3:10 pm, ndu...@gmail.com wrote:
> I want to write something like
> status_bit = (unsigned)(i - j) >> 31
>
> as an equivalent code for
signed int i;
signed int j;
> if(i < j){
> {
> status_bit = 1;
>
> }else{
> status_bit = 0;
> }
>
> This actually works for most of the cases but fails for two values
> i = 0x80000000
> j = 0x7fffffff
>
> I want a linear code for the above i.e. without jumps, so
> 1. what could be the issue?
> 2. what could be the solution?

ndun78@gmail.com wrote:
> I want to write something like
> status_bit = (unsigned)(i - j) >> 31
>
> as an equivalent code for
> if(i < j){
> {
> status_bit = 1;
> }else{
> status_bit = 0;
> }

Try the simple
status_bit = (i < j);

> This actually works for most of the cases but fails for two values
> i = 0x80000000
> j = 0x7fffffff
>
> I want a linear code for the above i.e. without jumps, so
> 1. what could be the issue?
> 2. what could be the solution?

Is there a reason for avoiding the obvious
status_bit = (i < j);
?

"Martin Ambuhl" <mambuhl@earthlink.net> a écrit dans le message de news:
5o0ngiFkk1juU1@mid.individual.net...
> ndun78@gmail.com wrote:
>> I want to write something like
>> status_bit = (unsigned)(i - j) >> 31
>>
>> as an equivalent code for
>> if(i < j){
>> {
>> status_bit = 1;
>> }else{
>> status_bit = 0;
>> }
>
> Try the simple
> status_bit = (i < j);
>
>> This actually works for most of the cases but fails for two values
>> i = 0x80000000
>> j = 0x7fffffff
>>
>> I want a linear code for the above i.e. without jumps, so
>> 1. what could be the issue?
>> 2. what could be the solution?
>
> Is there a reason for avoiding the obvious
> status_bit = (i < j);

In other words: if there is a way to compute this without tests and jumps,
the compiler should know.

--
Chqrlie.

> > Is there a reason for avoiding the obvious
> > status_bit = (i < j);
>
I think that it is not guaranteed to get only 1 or 0 as a result of i
< j, this may result in 0 or non zero value is it not?

ndun78@gmail.com wrote:

>
>> > Is there a reason for avoiding the obvious
>> > status_bit = (i < j);
>>
> I think that it is not guaranteed to get only 1 or 0 as a result of i
> < j, this may result in 0 or non zero value is it not?

No, the relational operators yield either 1 or 0.

> No, the relational operators yield either 1 or 0.
Is it guaranteed by ANSI C standard?

ndun78@gmail.com wrote:
>
> > > Is there a reason for avoiding the obvious
> > > status_bit = (i < j);
> >
> I think that it is not guaranteed to get only 1 or 0 as a result of i
> < j, this may result in 0 or non zero value is it not?

No.
(i < j) is can only be equal to either one or zero.

--
pete