John Reiser <[EMAIL PROTECTED]> wrote: > > If speed matters that much, then please recoup 33 cycles on x86 > by using shifts instead of three divides, such as (gcc 4.1.2): > > add_entropy_words(r, tmp, (bytes + 3) / 4); > > 0x8140689 <xfer_secondary_pool+206>: lea 0x3(%esi),%eax > 0x814068c <xfer_secondary_pool+209>: mov $0x4,%dl > 0x814068e <xfer_secondary_pool+211>: mov %edx,%edi > 0x8140690 <xfer_secondary_pool+213>: cltd > 0x8140691 <xfer_secondary_pool+214>: idiv %edi
There ought to be a warning about this sort of thing. [CHAR] random: Avoid signed integer division Joihn Reiser pointed out that we use signed integer divisions unnecessarily in random.c. This is bad because the C compiler is obliged to consider the case of a negative dividend. This patch changes all the relevant divisions and modulus operations to use unsigned arithmetic. Signed-off: Herbert Xu <[EMAIL PROTECTED]> Thanks, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} <[EMAIL PROTECTED]> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- diff --git a/drivers/char/random.c b/drivers/char/random.c index 5fee056..6c70bfb 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -694,11 +694,11 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes) if (r->pull && r->entropy_count < nbytes * 8 && r->entropy_count < r->poolinfo->POOLBITS) { /* If we're limited, always leave two wakeup worth's BITS */ - int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4; + int rsvd = r->limit ? 0 : random_read_wakeup_thresh / 4u; int bytes = nbytes; /* pull at least as many as BYTES as wakeup BITS */ - bytes = max_t(int, bytes, random_read_wakeup_thresh / 8); + bytes = max_t(int, bytes, random_read_wakeup_thresh / 8u); /* but never more than the buffer size */ bytes = min_t(int, bytes, sizeof(tmp)); @@ -707,8 +707,8 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes) r->name, bytes * 8, nbytes * 8, r->entropy_count); bytes=extract_entropy(r->pull, tmp, bytes, - random_read_wakeup_thresh / 8, rsvd); - add_entropy_words(r, tmp, (bytes + 3) / 4); + random_read_wakeup_thresh / 8u, rsvd); + add_entropy_words(r, tmp, (bytes + 3) / 4u); credit_entropy_store(r, bytes*8); } } @@ -739,14 +739,14 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min, nbytes * 8, r->name); /* Can we pull enough? */ - if (r->entropy_count / 8 < min + reserved) { + if (r->entropy_count / 8u < min + reserved) { nbytes = 0; } else { /* If limited, never pull more than available */ - if (r->limit && nbytes + reserved >= r->entropy_count / 8) - nbytes = r->entropy_count/8 - reserved; + if (r->limit && nbytes + reserved >= r->entropy_count / 8u) + nbytes = r->entropy_count / 8u - reserved; - if(r->entropy_count / 8 >= nbytes + reserved) + if(r->entropy_count / 8u >= nbytes + reserved) r->entropy_count -= nbytes*8; else r->entropy_count = reserved; @@ -781,7 +781,7 @@ static void extract_buf(struct entropy_store *r, __u8 *out) /* hash blocks of 16 words = 512 bits */ sha_transform(buf, (__u8 *)(r->pool + i), buf + 5); /* feed back portion of the resulting hash */ - add_entropy_words(r, &buf[i % 5], 1); + add_entropy_words(r, &buf[i % 5u], 1); } /* @@ -789,7 +789,7 @@ static void extract_buf(struct entropy_store *r, __u8 *out) * portion of the pool while mixing, and hash one * final time. */ - __add_entropy_words(r, &buf[i % 5], 1, data); + __add_entropy_words(r, &buf[i % 5u], 1, data); sha_transform(buf, (__u8 *)data, buf + 5); /* @@ -1040,7 +1040,7 @@ write_pool(struct entropy_store *r, const char __user *buffer, size_t count) count -= bytes; p += bytes; - add_entropy_words(r, buf, (bytes + 3) / 4); + add_entropy_words(r, buf, (bytes + 3) / 4u); } return 0; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
