Re: [PATCH 08/10] m68k: Add

Philippe De Muyter
2016-05-25T08:56:53Z

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

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 :)).

> + : "=&d" (a), "=&r" (b)
> + : "g" (x));
> +
> + return ((u16)(x*0x61c8) << 16) + a + b;
> +}

Just my two cents

Philippe