[glibc] string: Speed up strcasecmp test data initialization

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c1fb5d0e6b8d292ac526974d05c5adb4c3827fb0

commit c1fb5d0e6b8d292ac526974d05c5adb4c3827fb0
Author: Magnus Lindholm <[email protected]>
Date:   Wed Aug 5 23:14:59 2026 +0200

    string: Speed up strcasecmp test data initialization
    
    The strcasecmp and strncasecmp tests repeatedly initialize large
    buffers for many combinations of lengths and alignments.  The existing
    loops perform a remainder operation and call toupper and tolower for
    every element.
    
    Generate at most max_char elements using an additive recurrence and
    apply the case conversions while creating this initial pattern.  The
    recurrence produces the same sequence as the existing multiplication
    and remainder expression.  Expand the completed pattern using bulk
    copies.
    
    This preserves the generated test data and locale-dependent case
    conversion while substantially reducing the initialization cost on
    slower systems.
    
    Signed-off-by: Magnus Lindholm <[email protected]>
    Reviewed-by: Adhemerval Zanella <[email protected]>

Diff:
---
 string/test-strcasecmp.c  | 22 ++++++++++++++++++++--
 string/test-strncasecmp.c | 23 +++++++++++++++++++++--
 2 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/string/test-strcasecmp.c b/string/test-strcasecmp.c
index a5235fa1bb..d090dcbf36 100644
--- a/string/test-strcasecmp.c
+++ b/string/test-strcasecmp.c
@@ -63,6 +63,9 @@ 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 step = 23U % (size_t) max_char;
+  size_t pattern_len;
   char *s1, *s2;
 
   if (len == 0)
@@ -80,10 +83,25 @@ do_test (size_t align1, size_t align2, size_t len, int max_char,
   s1 = (char *) (buf1 + align1);
   s2 = (char *) (buf2 + align2);
 
-  for (i = 0; i < len; i++)
+  pattern_len
+    = len < (size_t) max_char ? len : (size_t) max_char;
+
+  for (i = 0; i < pattern_len; i++)
     {
-      s1[i] = toupper (1 + 23 * i % max_char);
+      s1[i] = toupper (1 + value);
       s2[i] = tolower (s1[i]);
+      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);
+      memcpy (s2 + i, s2, copy);
+      i += copy;
     }
 
   s1[len] = s2[len] = 0;
diff --git a/string/test-strncasecmp.c b/string/test-strncasecmp.c
index 035c680532..6b00113e66 100644
--- a/string/test-strncasecmp.c
+++ b/string/test-strncasecmp.c
@@ -83,6 +83,9 @@ do_test (size_t align1, size_t align2, size_t n, size_t len, int max_char,
 	 int exp_result)
 {
   size_t i;
+  size_t value = 0;
+  size_t step = 23U % (size_t) max_char;
+  size_t pattern_len;
   char *s1, *s2;
 
   if (len == 0)
@@ -100,10 +103,26 @@ do_test (size_t align1, size_t align2, size_t n, size_t len, int max_char,
   s1 = (char *) (buf1 + align1);
   s2 = (char *) (buf2 + align2);
 
-  for (i = 0; i < len; i++)
+  pattern_len
+    = len < (size_t) max_char ? len : (size_t) max_char;
+
+  for (i = 0; i < pattern_len; i++)
     {
-      s1[i] = toupper (1 + 23 * i % max_char);
+      s1[i] = toupper (1 + value);
       s2[i] = tolower (s1[i]);
+
+      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);
+      memcpy (s2 + i, s2, copy);
+      i += copy;
     }
 
   s1[len] = s2[len] = 0;