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Re: [PATCH] string/test-strncmp.c: Add comments within do_random_tests()
- From: Wainer dos Santos Moschetta <wainersm at linux dot vnet dot ibm dot com>
- To: libc-alpha at sourceware dot org
- Date: Thu, 30 Mar 2017 12:48:30 -0300
- Subject: Re: [PATCH] string/test-strncmp.c: Add comments within do_random_tests()
- Authentication-results: sourceware.org; auth=none
- References: <38bf371c-c7ae-8a5b-24f0-08d8ffce270f@us.ibm.com>
LGTM.
On 03/28/2017 05:06 PM, Paul Clarke wrote:
> I was about to throw this out after abandoning my attempts to "fix"
> string/test-strncmp.c (which didn't need fixing).
>
> However, since I added some comments which I found useful in
> navigating the code, I thought I should offer them for inclusion.
>
> -- 8< --
>
> I added comments and rearranged some code to clarify the workings
> of do_random_tests() in the hope that someone new to the code will
> find it much more comprehensible than I did.
>
> 2017-03-28 Paul A. Clarke <pc@us.ibm.com>
>
> * string/test-strncmp.c (do_random_tests): Add comments and rearrange
> some code for readability.
> ---
> string/test-strncmp.c | 40 +++++++++++++++++++++++++++++++++++++---
> 1 file changed, 37 insertions(+), 3 deletions(-)
>
> diff --git a/string/test-strncmp.c b/string/test-strncmp.c
> index fe3c4e3..dabf1f1 100644
> --- a/string/test-strncmp.c
> +++ b/string/test-strncmp.c
> @@ -270,33 +270,58 @@ do_random_tests (void)
> size_t i, j, n, align1, align2, pos, len1, len2, size;
> int result;
> long r;
> + /* Get pointers near the end of a "page". */
> UCHAR *p1 = (UCHAR *) (buf1 + page_size - 512 * CHARBYTES);
> UCHAR *p2 = (UCHAR *) (buf2 + page_size - 512 * CHARBYTES);
>
> for (n = 0; n < ITERATIONS; n++)
> {
> + /* Start index for first string within p1. */
> align1 = random () & 31;
> +
> + /* Start index for second string within p2. */
> if (random () & 1)
> align2 = random () & 31;
> else
> align2 = align1 + (random () & 24);
> - pos = random () & 511;
> - size = random () & 511;
> +
> + /* Compute larger offset into buffers. */
> j = align1 > align2 ? align1 : align2;
> - if (pos + j >= 511)
> +
> + /* Position of difference between strings. */
> + pos = random () & 511;
> +
> + /* Ensure pos within range for strings. */
> + if (j + pos >= 511)
> pos = 510 - j - (random () & 7);
> +
> + /* Maximum size of operation. */
> + size = random () & 511;
> +
> + /* Note: size does not need to be capped to the page boundary, as either
> + - size >= pos, so the null ('\0') at 'pos' will terminate strncmp, or
> + - size < pos, so 'size' will terminate strncmp. */
> +
> + /* Actual length of 1st string. */
> len1 = random () & 511;
> if (pos >= len1 && (random () & 1))
> len1 = pos + (random () & 7);
> if (len1 + j >= 512)
> len1 = 511 - j - (random () & 7);
> +
> + /* Actual length of 2nd string. */
> + /* Note: len2 >= len1. */
> if (pos >= len1)
> len2 = len1;
> else
> len2 = len1 + (len1 != 511 - j ? random () % (511 - j - len1) : 0);
> +
> + /* Compute max length of strings, plus margin of dword. */
> j = (pos > len2 ? pos : len2) + align1 + 64;
> if (j > 512)
> j = 512;
> +
> + /* Fill p1 with random data. */
> for (i = 0; i < j; ++i)
> {
> p1[i] = random () & 255;
> @@ -307,6 +332,8 @@ do_random_tests (void)
> p1[i] = 1 + (random () & 127);
> }
> }
> +
> + /* Fill p2 with random data. */
> for (i = 0; i < j; ++i)
> {
> p2[i] = random () & 255;
> @@ -319,11 +346,15 @@ do_random_tests (void)
> }
>
> result = 0;
> +
> + /* Make strings the same, up to position pos. */
> MEMCPY (p2 + align2, p1 + align1, pos);
> +
> if (pos < len1)
> {
> if (p2[align2 + pos] == p1[align1 + pos])
> {
> + /* Insert difference. */
> p2[align2 + pos] = random () & 255;
> if (p2[align2 + pos] == p1[align1 + pos])
> p2[align2 + pos] = p1[align1 + pos] + 3 + (random () & 127);
> @@ -331,12 +362,15 @@ do_random_tests (void)
>
> if (pos < size)
> {
> + /* Set expectations. */
> if (p1[align1 + pos] < p2[align2 + pos])
> result = -1;
> else
> result = 1;
> }
> }
> +
> + /* Null terminate strings. */
> p1[len1 + align1] = 0;
> p2[len2 + align2] = 0;
>