[9fans] fun question

[ron minnich]

I ask this every time I hit this piece of code, I think. But what the heck:

  if(seed - 0)
seed = seed + m_31;

what's wrong with this code?

ron

Re: [9fans] fun question

[erik quanstrom]

On Thu Jan 22 15:55:09 EST 2009, rminn...@gmail.com wrote:
 I ask this every time I hit this piece of code, I think. But what the heck:
 
   if(seed - 0)
 seed = seed + m_31;
 
 what's wrong with this code?

supposing the code does what it is supposed
to on some machines, i would guess that this
could be a problem for sign-magnitude or one's-comp.
machines, since 0 and -0 are different.  if that's
the case, one would guess that the object is to clear
sign bit and -0 is the failure case.

then again, that's a very wild guess and one
would assume that sign = -sign would be
better.

-0 is a strange construction and the spacing
is misleading. it's interesting that atoi(2) and
the differ on - 0.

- erik

Re: [9fans] fun question

[Russ Cox]

On Thu, Jan 22, 2009 at 12:53 PM, ron minnich rminn...@gmail.com wrote:
 I ask this every time I hit this piece of code, I think. But what the heck:

  if(seed - 0)
seed = seed + m_31;

 what's wrong with this code?

- is a unary operator.

russ

Re: [9fans] fun question

[Pietro Gagliardi]

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On Jan 22, 2009, at 5:01 PM, Russ Cox wrote:

- is a unary operator.



okay, what does it do? (unless you meant - in C++)


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Re: [9fans] fun question

[Russ Cox]

 - is a unary operator.

 okay, what does it do? (unless you meant - in C++)

it receives from a channel.

russ

Re: [9fans] fun question

[erik quanstrom]

On Thu Jan 22 17:55:55 EST 2009, r...@swtch.com wrote:
  - is a unary operator.
 
  okay, what does it do? (unless you meant - in C++)
 
 it receives from a channel.

i assumed that ron was talking about c.
in c, - 0 tokenizes as , -, and 0.
- is taken to be a unary operator on 0.

even gcc does this correctly:

; cat  x.c
#include u.h
#include libc.h

void
x(int seed)
{
int m_31;

m_31 = 131;
if(seed - 0)
seed = seed + m_31;
print(seed %d\n, seed);
}

void
main(void)
{
x(-5);
exits();
}
eot; 9c x.c
; 9l x.o
; ./a.out
seed -2147483648

- erik

Re: [9fans] fun question

[ron minnich]

Erik got it. That code originally was written for a 1s complement
machine, the CDC 7200 I believe. I get a kick out of it every time I
see something and remember machines with + and - 0 :-)

ron

Re: [9fans] fun question

[Pietro Gagliardi]

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On Jan 22, 2009, at 6:01 PM, erik quanstrom wrote:


i assumed that ron was talking about c.


Yeah, that's what I thought. Sorry, Russ.

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