[glibc/release/2.44/master] string: Speed up strcmp test data initialization

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=65d35639a9d055e423345c8748908c8aa48b19b9

commit 65d35639a9d055e423345c8748908c8aa48b19b9
Author: Magnus Lindholm <[email protected]>
Date:   Wed Aug 5 23:14:58 2026 +0200

    string: Speed up strcmp test data initialization
    
    The strcmp and strncmp tests repeatedly initialize large buffers for
    many combinations of lengths and alignments.  The existing loops
    perform a remainder operation and two individual stores for every
    element.
    
    Generate at most max_char elements using an additive recurrence.  The
    recurrence produces the same sequence as the existing multiplication
    and remainder expression.  Expand this initial pattern using bulk
    copies, and then copy the completed first buffer to the second buffer.
    
    This preserves the generated test data while substantially reducing
    the initialization cost on slower systems.
    
    The change also applies to the wcscmp and wcsncmp tests, which include
    the same test sources.
    
    Signed-off-by: Magnus Lindholm <[email protected]>
    Reviewed-by: Adhemerval Zanella <[email protected]>
    (cherry picked from commit 9b323b95567dff46b34157ac4455734633921abb)

Diff:
---
 string/test-strcmp.c  | 28 ++++++++++++++++++++++++++--
 string/test-strncmp.c | 28 ++++++++++++++++++++++++++--
 2 files changed, 52 insertions(+), 4 deletions(-)

diff --git a/string/test-strcmp.c b/string/test-strcmp.c
index 76ccff46e2..ca52827b11 100644
--- a/string/test-strcmp.c
+++ b/string/test-strcmp.c
@@ -156,6 +156,10 @@ do_test (size_t align1, size_t align2, size_t len, int max_char,
          int exp_result)
 {
   size_t i;
+  size_t value = 0;
+  size_t pattern_len;
+  size_t step
+    = (23U << ((CHARBYTES - 1) * 8)) % (size_t) max_char;
 
   CHAR *s1, *s2;
 
@@ -179,8 +183,28 @@ do_test (size_t align1, size_t align2, size_t len, int max_char,
   i = align2 + CHARBYTES * (len + 2);
   s2 = (CHAR *)(buf2 + ((page_size - i) / 16 * 16) + align2);
 
-  for (i = 0; i < len; i++)
-    s1[i] = s2[i] = 1 + (23 << ((CHARBYTES - 1) * 8)) * i % max_char;
+  /* The generated sequence repeats after at most max_char elements.  */
+  pattern_len
+    = len < (size_t) max_char ? len : (size_t) max_char;
+
+  for (i = 0; i < pattern_len; i++)
+    {
+      s1[i] = 1 + value;
+
+      value += step;
+      if (value >= (size_t) max_char)
+        value -= max_char;
+    }
+
+  while (i < len)
+    {
+      size_t copy = i < len - i ? i : len - i;
+
+      MEMCPY (s1 + i, s1, copy);
+      i += copy;
+    }
+
+  MEMCPY (s2, s1, len);
 
   s1[len] = s2[len] = 0;
   s1[len + 1] = 23;
diff --git a/string/test-strncmp.c b/string/test-strncmp.c
index 54ada39eb2..9da0f21f60 100644
--- a/string/test-strncmp.c
+++ b/string/test-strncmp.c
@@ -190,6 +190,9 @@ do_test_n (size_t align1, size_t align2, size_t len, size_t n, int n_in_bounds,
 {
   size_t i, buf_bound;
   CHAR *s1, *s2, *s1_end, *s2_end;
+  size_t value = 0;
+  size_t pattern_len;
+  size_t step = (23U << ((CHARBYTES - 1) * 8)) % (size_t) max_char;
 
   align1 &= ~(CHARBYTES - 1);
   align2 &= ~(CHARBYTES - 1);
@@ -216,8 +219,29 @@ do_test_n (size_t align1, size_t align2, size_t len, size_t n, int n_in_bounds,
       s2[n] = 23;
     }
 
-  for (i = 0; i < buf_bound; i++)
-    s1[i] = s2[i] = 1 + (23 << ((CHARBYTES - 1) * 8)) * i % max_char;
+  /* The generated sequence repeats after at most max_char elements.  */
+  pattern_len
+    = buf_bound < (size_t) max_char
+      ? buf_bound : (size_t) max_char;
+
+  for (i = 0; i < pattern_len; i++)
+    {
+      s1[i] = 1 + value;
+
+      value += step;
+      if (value >= (size_t) max_char)
+        value -= max_char;
+    }
+
+  while (i < buf_bound)
+    {
+      size_t copy = i < buf_bound - i ? i : buf_bound - i;
+
+      MEMCPY (s1 + i, s1, copy);
+      i += copy;
+    }
+
+  MEMCPY (s2, s1, buf_bound);
 
   s1[len] = 0;
   s2[len] = 0;