Messages in this thread | | | Date | Thu, 24 Jan 2002 16:55:48 -0500 (EST) | From | "Richard B. Johnson" <> | Subject | Re: RFC: booleans and the kernel |
| |
On Thu, 24 Jan 2002, Oliver Xymoron wrote:
> On Thu, 24 Jan 2002, Richard B. Johnson wrote: > > > On Thu, 24 Jan 2002, Oliver Xymoron wrote: > > > > > On Thu, 24 Jan 2002, Jeff Garzik wrote: > > > > > > > A small issue... > > > > > > > > C99 introduced _Bool as a builtin type. The gcc patch for it went into > > > > cvs around Dec 2000. Any objections to propagating this type and usage > > > > of 'true' and 'false' around the kernel? > > > > > > Ugh, no. C doesn't need booleans, neither do Perl or Python. This is a > > > sickness imported from _recent_ C++ by way of Java by way of Pascal. This > > > just complicates things. > > > > > > > Where variables are truly boolean use of a bool type makes the > > > > intentions of the code more clear. And it also gives the compiler a > > > > slightly better chance to optimize code [I suspect]. > > > > > > Unlikely. The compiler can already figure this sort of thing out from > > > context. > > > > IFF the 'C' compiler code-generators start making better code, i.e., > > ORing a value already in a register, with itself and jumping on > > condition, then bool will be helpful. Right now, I see tests against > > numbers (like 0). This increases the code-size because the 0 is > > in the instruction stream, plus the comparison of an immediate > > value to a register value (on Intel) takes more CPU cycles. > > The compiler _will_ turn if(a==0) into a test of a with itself rather than > a comparison against a constant. Since PDP days, no doubt.
Don't you wish!
int foo(int i) {
if(i) return 0; else return 1; }
.file "xxx.c" .version "01.01" gcc2_compiled.: .text .align 4 .globl foo .type foo,@function foo: pushl %ebp movl %esp,%ebp cmpl $0,8(%ebp) <-------------- Compare against zero. je .L2 xorl %eax,%eax jmp .L1 jmp .L3 .align 4 .L2: movl $1,%eax jmp .L1 .align 4 .L3: .L1: movl %ebp,%esp popl %ebp ret .Lfe1: .size foo,.Lfe1-foo .ident "GCC: (GNU) egcs-2.91.66 19990314 (egcs-1.1.2 release)"
Cheers, Dick Johnson
Penguin : Linux version 2.4.1 on an i686 machine (797.90 BogoMips).
I was going to compile a list of innovations that could be attributed to Microsoft. Once I realized that Ctrl-Alt-Del was handled in the BIOS, I found that there aren't any.
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |