[v4 PATCH] sha2: new header <sha2.h>

[Richard Henderson]

On 04/07/2015 06:02 PM, Shawn Landden wrote:
> +#if _STRING_ARCH_unaligned
> +
> +#define put_be32(p, v)	do { *(uint32_t *)(p) = be32toh(v); } while (0)
> +#define put_be64(p, v)	do { *(uint64_t *)(p) = be64toh(v); } while (0)
> +
> +#else
> +
> +#define put_be32(p, v)	do { \
> +	unsigned uint32_t __v = (v); \
> +	*((unsigned char *)(p) + 0) = __v >> 24; \
> +	*((unsigned char *)(p) + 1) = __v >> 16; \
> +	*((unsigned char *)(p) + 2) = __v >>  8; \
> +	*((unsigned char *)(p) + 3) = __v >>  0; } while (0)
> +#define put_be64(p, v)	do { \
> +	unsigned uint64_t __v = (v); \
> +	*((unsigned char *)(p) + 0) = __v >> 56; \
> +	*((unsigned char *)(p) + 1) = __v >> 48; \
> +	*((unsigned char *)(p) + 2) = __v >> 40; \
> +	*((unsigned char *)(p) + 3) = __v >> 32; \
> +	*((unsigned char *)(p) + 4) = __v >> 24; \
> +	*((unsigned char *)(p) + 5) = __v >> 16; \
> +	*((unsigned char *)(p) + 6) = __v >>  8; \
> +	*((unsigned char *)(p) + 7) = __v >>  0; } while (0)
> +
> +#endif

Is there an extremely good reason why you're using macros instead of inline
functions here?

Storing through a packed structure is the easiest way to make gcc produce what
you want, without having to make every port define _STRING_ARCH_unaligned.

E.g.

static inline void put_be32(void *p, uint32_t v)
{
  struct __attribute__((packed, may_alias)) { uint32_t x; } *u = p;
  u->x = be32toh(v);
}

This should produce significantly better code for any gcc target that normally
requires alignment but implements the movmem pattern.  Especially Alpha (using
stq_u) and mips (using swl, swr).


r~