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Date: Sat, 9 Jul 2022 14:27:45 +0200
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Yury Norov <yury.norov@...il.com>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] lib/bitmap: Make parameter len unsigned
Dear Yuri,
Thank you for your reply, and sorry for all the failure messages the
first version created.
Am 08.07.22 um 16:38 schrieb Yury Norov:
> On Fri, Jul 08, 2022 at 09:52:40AM +0200, Paul Menzel wrote:
>> The length is non-negative, so make it unsigned.
>>
>> Signed-off-by: Paul Menzel <pmenzel@...gen.mpg.de>
> Can you please tell more about your motivation for fixing
> __bitmap_set?
It’s just about semantics(?) that a count can’t be negative, and only
seems to generate tiny smaller code (less instructions):
```
__bitmap_set:
__bitmap_set:
movl %esi, %eax
movl %esi, %eax
movq %rdi, %r8 <
movl %esi, %ecx
movl %esi, %ecx
movl %edx, %edi |
movl %esi, %r8d
>
movl $64, %esi
>
andl $63, %ecx
shrl $6, %eax
shrl $6, %eax
andl $63, %esi |
movl %edx, %r9d
movq $-1, %rdx |
leaq (%rdi,%rax,8), %rax
leaq (%r8,%rax,8), %rax |
subl %ecx, %esi
leal -64(%rsi,%rdi), %r8d |
movq $-1, %rdi
salq %cl, %rdx |
salq %cl, %rdi
testl %r8d, %r8d |
cmpl %edx, %esi
js .L88 |
ja .L85
movl %r8d, %r9d <
shrl $6, %r9d <
leal 1(%r9), %esi <
leaq (%rax,%rsi,8), %rsi <
.L86: .L86:
orq %rdx, (%rax) |
subl %esi, %edx
>
orq %rdi, (%rax)
>
movl $64, %esi
addq $8, %rax
addq $8, %rax
movq $-1, %rdx |
movq $-1, %rdi
cmpq %rsi, %rax |
cmpl $63, %edx
jne .L86 |
ja .L86
sall $6, %r9d <
subl %r9d, %r8d <
.L85: .L85:
testl %r8d, %r8d |
testl %edx, %edx
je .L84
je .L84
addl %edi, %ecx |
leal (%r8,%r9), %ecx
movq $-1, %rax |
movq $-1, %rdx
negl %ecx
negl %ecx
shrq %cl, %rax |
shrq %cl, %rdx
andq %rax, %rdx |
andq %rdx, %rdi
orq %rdx, (%rsi) |
orq %rdi, (%rax)
.L84: .L84:
ret ret
.L88: <
movq %rax, %rsi <
movl %edi, %r8d <
jmp .L85 <
.size __bitmap_set, .-__bitmap_set
.size __bitmap_set, .-__bitmap_set
.p2align 4
.p2align 4
.globl __bitmap_clear
.globl __bitmap_clear
.type __bitmap_clear, @function
.type __bitmap_clear, @function
```
$ diff lib/bitmap.1.S lib/bitmap.2.S | diffstat
unknown | 55 ++++++++++++++++++++++++-------------------------------
1 file changed, 24 insertions(+), 31 deletions(-)
> The following __bitmap_clear has the same problem, and
> bitmap_parse{,_user}, and bitmap_print_to_pagebuf, and
> bitmap_parselist...
Indeed.
> Is there a particular problem that is resolved after fixing
> __bitmap_set()?
>
> I'm OK if this is a single patch, but for a cleanup work it would be
> more logical to clean everything in a single patch/series...
If you agree, I can change the other places too.
Kind regards,
Paul
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