Implemented rand(), rand_r() and srand() using a simple Linear Congruential Generator.

2 files changed, 64 insertions, 0 deletions

diff --git a/src/library.js b/src/library.js
index 634f98dc..a7ac6fc0 100644
--- a/src/library.js
+++ b/src/library.js
@@ -3472,6 +3472,28 @@ LibraryManager.library = {
     return limit;
   },
 
+  // A glibc-like implementation of the C random number generation functions:
+  //   http://pubs.opengroup.org/onlinepubs/000095399/functions/rand.html
+  __rand_state: 42,
+  srand__deps: ['__rand_state'],
+  srand: function(seed) {
+    // void srand(unsigned seed);
+    ___rand_state = seed;
+  },
+  rand__deps: ['__rand_state'],
+  rand: function() {
+    // int rand(void);
+    ___rand_state = (1103515245 * ___rand_state + 12345) % 0x100000000;
+    return ___rand_state & 0x7FFFFFFF;
+  },
+  rand_r: function(seed) {
+    // int rand_r(unsigned *seed);
+    var state = {{{ makeGetValue('seed', 0, 'i32') }}};
+    state = (1103515245 * state + 12345) % 0x100000000;
+    {{{ makeSetValue('seed', 0, 'state', 'i32') }}}
+    return state & 0x7FFFFFFF;
+  },
+
   // ==========================================================================
   // string.h
   // ==========================================================================
diff --git a/tests/runner.py b/tests/runner.py
index 438726af..77aa0d4f 100644
--- a/tests/runner.py
+++ b/tests/runner.py
@@ -2043,6 +2043,48 @@ if 'benchmark' not in sys.argv:
                    output_nicerizer=lambda x: x.replace('\n', '*'),
                    post_build=add_pre_run_and_checks)
 
+    def test_rand(self):
+      src = r'''
+        #include <stdio.h>
+        #include <stdlib.h>
+
+        int main() {
+          printf("%d\n", rand());
+          printf("%d\n", rand());
+
+          srand(123);
+          printf("%d\n", rand());
+          printf("%d\n", rand());
+          srand(123);
+          printf("%d\n", rand());
+          printf("%d\n", rand());
+
+          unsigned state = 0;
+          int r;
+          r = rand_r(&state);
+          printf("%d, %u\n", r, state);
+          r = rand_r(&state);
+          printf("%d, %u\n", r, state);
+          state = 0;
+          r = rand_r(&state);
+          printf("%d, %u\n", r, state);
+
+          return 0;
+        }
+        '''
+      expected = '''
+        1250496027
+        1116302336
+        440917656
+        1476150784
+        440917656
+        1476150784
+        12345, 12345
+        1406932606, 3554416254
+        12345, 12345
+        '''
+      self.do_test(src, re.sub(r'(^|\n)\s+', r'\1', expected))
+
     def test_strtod(self):
       src = r'''
         #include <stdio.h>