From: Matt Mackall The add_ptr variable wasn't used in a sensible way, use only i instead. i got reused later for a different purpose, use j instead. While we're here, put tap0 first in the tap list and add a comment. Signed-off-by: Matt Mackall Cc: Theodore Ts'o Signed-off-by: Andrew Morton --- drivers/char/random.c | 21 ++++++++++----------- 1 file changed, 10 insertions(+), 11 deletions(-) diff -puN drivers/char/random.c~random-simplify-add_ptr-logic drivers/char/random.c --- a/drivers/char/random.c~random-simplify-add_ptr-logic +++ a/drivers/char/random.c @@ -454,7 +454,7 @@ static void __add_entropy_words(struct e static __u32 const twist_table[8] = { 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158, 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 }; - unsigned long i, add_ptr, tap1, tap2, tap3, tap4, tap5; + unsigned long i, j, tap1, tap2, tap3, tap4, tap5; int input_rotate; int wordmask = r->poolinfo->poolwords - 1; __u32 w; @@ -469,19 +469,21 @@ static void __add_entropy_words(struct e spin_lock_irqsave(&r->lock, flags); input_rotate = r->input_rotate; - add_ptr = r->add_ptr; + i = r->add_ptr; while (nwords--) { w = rol32(*in++, input_rotate & 31); - i = add_ptr = (add_ptr - 1) & wordmask; + i = (i - 1) & wordmask; /* XOR in the various taps */ + w ^= r->pool[i]; w ^= r->pool[(i + tap1) & wordmask]; w ^= r->pool[(i + tap2) & wordmask]; w ^= r->pool[(i + tap3) & wordmask]; w ^= r->pool[(i + tap4) & wordmask]; w ^= r->pool[(i + tap5) & wordmask]; - w ^= r->pool[i]; + + /* Mix the result back in with a twist */ r->pool[i] = (w >> 3) ^ twist_table[w & 7]; /* @@ -494,14 +496,11 @@ static void __add_entropy_words(struct e } r->input_rotate = input_rotate; - r->add_ptr = add_ptr; + r->add_ptr = i; - if (out) { - for (i = 0; i < 16; i++) { - out[i] = r->pool[add_ptr]; - add_ptr = (add_ptr - 1) & wordmask; - } - } + if (out) + for (j = 0; j < 16; j++) + out[j] = r->pool[(i - j) & wordmask]; spin_unlock_irqrestore(&r->lock, flags); } _