[freetype2] master 8fb9d22: [ftfuzzer] Replace `rand' with an xorshift algorithm.

[Werner LEMBERG]

branch: master
commit 8fb9d22a6b0131f05490d6314a28f141ab1eb85f
Author: Werner Lemberg <address@hidden>
Commit: Werner Lemberg <address@hidden>

    [ftfuzzer] Replace `rand' with an xorshift algorithm.
    
    * src/tools/ftfuzzer/ftfuzzer.cc: Don't include `stdlib.h'.
    (Random): Implement and use a 32bit `xorshift' algorithm.
---
 ChangeLog                      |    7 +++++++
 src/tools/ftfuzzer/ftfuzzer.cc |   18 +++++++++++++-----
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 91a30e6..8cbe68f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 2016-12-30  Werner Lemberg  <address@hidden>
 
+       [ftfuzzer] Replace `rand' with an xorshift algorithm.
+
+       * src/tools/ftfuzzer/ftfuzzer.cc: Don't include `stdlib.h'.
+       (Random): Implement and use a 32bit `xorshift' algorithm.
+
+2016-12-30  Werner Lemberg  <address@hidden>
+
        [ftfuzzer] Restrict number of tested bitmap strikes.
 
        Malformed fonts often have large values for the number of bitmap
diff --git a/src/tools/ftfuzzer/ftfuzzer.cc b/src/tools/ftfuzzer/ftfuzzer.cc
index 535be3f..31834a5 100644
--- a/src/tools/ftfuzzer/ftfuzzer.cc
+++ b/src/tools/ftfuzzer/ftfuzzer.cc
@@ -22,7 +22,6 @@
 
 #include <assert.h>
 #include <stdint.h>
-#include <stdlib.h>
 
 #include <memory>
 #include <vector>
@@ -88,6 +87,8 @@
     int  t; // total number of values so far
     int  m; // number of selected values so far
 
+    uint32_t  r; // the current pseudo-random number
+
     Random( int n_,
             int N_ )
     : n( n_ ),
@@ -96,10 +97,10 @@
       t = 0;
       m = 0;
 
-      // ideally, this should depend on the input file,
+      // Ideally, this should depend on the input file,
       // for example, taking the sha256 as input;
-      // however, this is overkill for fuzzying tests
-      srand( 12345 );
+      // however, this is overkill for fuzzying tests.
+      r = 12345;
     }
 
     int get()
@@ -108,7 +109,14 @@
         return -1;
 
     Redo:
-      double  U = double(rand()) / RAND_MAX;
+      // We can't use `rand': different C libraries might provide
+      // different implementations of this function.  As a replacement,
+      // we use a 32bit version of the `xorshift' algorithm.
+      r ^= r << 13;
+      r ^= r >> 17;
+      r ^= r << 5;
+
+      double  U = double( r ) / UINT32_MAX;
 
       if ( ( N - t ) * U >= ( n - m ) )
       {