Optimize and simplify __str_base10() by removing temporary buffer

Eliminate the temporary tmp[] buffer in __str_base10() by writing
digits directly into the output buffer. This avoids an extra memory
copy and improves efficiency while keeping the logic simple. The
maximum digit count comment is also removed as it is no longer
relevant.

Author: visitorckw

lib/libc.c

@@ -470,9 +470,6 @@ static char *__str_base10(uint32_t value, char *buffer, int *length)
         *length = 1;
         return buffer;
     }
-
-    /* Max digits for 32-bit: 4,294,967,295 (10 digits) + sign + null */
-    char tmp[12];
     int pos = 0;
 
     while (value > 0) {
@@ -488,15 +485,10 @@ static char *__str_base10(uint32_t value, char *buffer, int *length)
         q += t;
         r -= (((t << 2) + t) << 1);
 
-        tmp[pos++] = '0' + r;
+        buffer[pos++] = '0' + r;
         value = q;
     }
-
-    /* Reverse digits into output buffer */
     *length = pos;
-    for (int i = 0; i < pos; i++) {
-        buffer[i] = tmp[i];
-    }
 
     return buffer;
 }