Messages in this thread | | | Date | 25 May 2016 05:14:35 -0400 | From | "George Spelvin" <> | Subject | Re: [PATCH 08/10] m68k: Add <asm/archhash.h> |
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> On Wed, May 25, 2016 at 03:34:55AM -0400, George Spelvin wrote: >> +static inline u32 __attribute_const__ __hash_32(u32 x) >> +{ >> + u32 a, b; >> + >> + asm( "move.l %2,%0" /* 0x0001 */ >> + "\n lsl.l #2,%0" /* 0x0004 */ >> + "\n move.l %0,%1" >> + "\n lsl.l #7,%0" /* 0x0200 */ >> + "\n add.l %2,%0" /* 0x0201 */ >> + "\n add.l %0,%1" /* 0x0205 */ >> + "\n add.l %0,%0" /* 0x0402 */ >> + "\n add.l %0,%1" /* 0x0607 */ >> + "\n lsl.l #5,%0" /* 0x8040 */ >> + /* 0x8647 */
> There is no standard way to write asm in the kernel, but I prefer > a simple semicolon after each insn
I did it the way I did above because it makes the gcc -S output very legible. Just like I put a space before the perands on m68k but a tab on h8300: that's what GCC does on those platforms.
I started with the "\n\t" suffixes on each line like so much other kernel code, but then figured out the format above which is legible both in C source and compiler output.
>> asm("move.l %2,%0;" /* 0x0001 */ >> "lsl.l #2,%0;" /* 0x0004 */ >> "move.l %0,%1;" >> "lsl.l #7,%0;" /* 0x0200 */ >> "add.l %2,%0;" /* 0x0201 */ >> "add.l %0,%1;" /* 0x0205 */ >> "add.l %0,%0;" /* 0x0402 */ >> "add.l %0,%1;" /* 0x0607 */ >> "lsl.l #5,%0" /* 0x8040 */ >> /* 0x8647 */
> Also, it took me some time to understand the hexadecimal constants > in the comments (and the last one predicts a future event :)).
Can you recmmend a better way to comment this? My nose is so deep in the code it's hard for me to judge.
> Just my two cents
And thank you very much for them!
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