Re: [PATCH 2/2] ffsl, ffsll: new modules

[Bruno Haible]

Eric Blake wrote:
> * modules/ffsl-tests: New test file.
> * modules/ffsll-tests: Likewise.
> * tests/test-ffsl.c: Likewise.
> * tests/test-ffsll.c: Likewise.

It doesn't hurt to clarify how these functions work on bit patterns that
represent "negative" numbers and have more than one bit set.


2011-07-15  Bruno Haible  <address@hidden>

        ffs: More tests.
        * tests/test-ffs.c (NBITS): New macro.
        (main): Add more tests.
        * tests/test-ffsl.c (NBITS): New macro.
        (main): Add more tests.
        * tests/test-ffsll.c (NBITS): New macro.
        (main): Add more tests.

--- tests/test-ffs.c.orig       Sat Jul 16 02:33:54 2011
+++ tests/test-ffs.c    Sat Jul 16 02:32:00 2011
@@ -26,11 +26,13 @@
 
 #include "macros.h"
 
+#define NBITS (sizeof (int) * CHAR_BIT)
+
 static int
 naive (int i)
 {
   unsigned int j;
-  for (j = 0; j < CHAR_BIT * sizeof i; j++)
+  for (j = 0; j < NBITS; j++)
     if (i & (1U << j))
       return j + 1;
   return 0;
@@ -39,14 +41,28 @@
 int
 main (int argc, char *argv[])
 {
+  int x;
   int i;
 
-  for (i = -128; i <= 128; i++)
-    ASSERT (ffs (i) == naive (i));
-  for (i = 0; i < CHAR_BIT * sizeof i; i++)
+  for (x = -128; x <= 128; x++)
+    ASSERT (ffs (x) == naive (x));
+  for (i = 0; i < NBITS; i++)
     {
       ASSERT (ffs (1U << i) == naive (1U << i));
       ASSERT (ffs (1U << i) == i + 1);
+      ASSERT (ffs (-1U << i) == i + 1);
+    }
+  for (i = 0; i < NBITS - 1; i++)
+    {
+      ASSERT (ffs (3U << i) == i + 1);
+      ASSERT (ffs (-3U << i) == i + 1);
+    }
+  for (i = 0; i < NBITS - 2; i++)
+    {
+      ASSERT (ffs (5U << i) == i + 1);
+      ASSERT (ffs (-5U << i) == i + 1);
+      ASSERT (ffs (7U << i) == i + 1);
+      ASSERT (ffs (-7U << i) == i + 1);
     }
   return 0;
 }
--- tests/test-ffsl.c.orig      Sat Jul 16 02:33:54 2011
+++ tests/test-ffsl.c   Sat Jul 16 02:32:24 2011
@@ -26,11 +26,13 @@
 
 #include "macros.h"
 
+#define NBITS (sizeof (long int) * CHAR_BIT)
+
 static int
 naive (long int i)
 {
   unsigned long int j;
-  for (j = 0; j < CHAR_BIT * sizeof i; j++)
+  for (j = 0; j < NBITS; j++)
     if (i & (1UL << j))
       return j + 1;
   return 0;
@@ -39,14 +41,28 @@
 int
 main (int argc, char *argv[])
 {
-  long int i;
+  long int x;
+  int i;
 
   for (i = -128; i <= 128; i++)
     ASSERT (ffsl (i) == naive (i));
-  for (i = 0; i < CHAR_BIT * sizeof i; i++)
+  for (i = 0; i < NBITS; i++)
     {
       ASSERT (ffsl (1UL << i) == naive (1UL << i));
       ASSERT (ffsl (1UL << i) == i + 1);
+      ASSERT (ffsl (-1UL << i) == i + 1);
+    }
+  for (i = 0; i < NBITS - 1; i++)
+    {
+      ASSERT (ffsl (3UL << i) == i + 1);
+      ASSERT (ffsl (-3UL << i) == i + 1);
+    }
+  for (i = 0; i < NBITS - 2; i++)
+    {
+      ASSERT (ffsl (5UL << i) == i + 1);
+      ASSERT (ffsl (-5UL << i) == i + 1);
+      ASSERT (ffsl (7UL << i) == i + 1);
+      ASSERT (ffsl (-7UL << i) == i + 1);
     }
   return 0;
 }
--- tests/test-ffsll.c.orig     Sat Jul 16 02:33:54 2011
+++ tests/test-ffsll.c  Sat Jul 16 02:32:38 2011
@@ -26,11 +26,13 @@
 
 #include "macros.h"
 
+#define NBITS (sizeof (long long int) * CHAR_BIT)
+
 static int
 naive (long long int i)
 {
   unsigned long long int j;
-  for (j = 0; j < CHAR_BIT * sizeof i; j++)
+  for (j = 0; j < NBITS; j++)
     if (i & (1ULL << j))
       return j + 1;
   return 0;
@@ -39,14 +41,28 @@
 int
 main (int argc, char *argv[])
 {
-  long long int i;
+  long long int x;
+  int i;
 
-  for (i = -128; i <= 128; i++)
-    ASSERT (ffsll (i) == naive (i));
-  for (i = 0; i < CHAR_BIT * sizeof i; i++)
+  for (x = -128; x <= 128; x++)
+    ASSERT (ffsll (x) == naive (x));
+  for (i = 0; i < NBITS; i++)
     {
       ASSERT (ffsll (1ULL << i) == naive (1ULL << i));
       ASSERT (ffsll (1ULL << i) == i + 1);
+      ASSERT (ffsll (-1ULL << i) == i + 1);
+    }
+  for (i = 0; i < NBITS - 1; i++)
+    {
+      ASSERT (ffsll (3ULL << i) == i + 1);
+      ASSERT (ffsll (-3ULL << i) == i + 1);
+    }
+  for (i = 0; i < NBITS - 2; i++)
+    {
+      ASSERT (ffsll (5ULL << i) == i + 1);
+      ASSERT (ffsll (-5ULL << i) == i + 1);
+      ASSERT (ffsll (7ULL << i) == i + 1);
+      ASSERT (ffsll (-7ULL << i) == i + 1);
     }
   return 0;
 }


-- 
In memoriam Natalya Estemirova <http://en.wikipedia.org/wiki/Natalya_Estemirova>