Add bitReverse

.github/workflows/classroom.yml

@@ -260,6 +260,19 @@ jobs:
         comparison-method: contains
         timeout: 10
         max-score: 2
+    - name: bitReverse
+      id: bitreverse
+      uses: classroom-resources/autograding-io-grader@v1
+      with:
+        test-name: bitReverse
+        setup-command: sudo apt-get install gcc-multilib && make clean
+          && make all
+        command: ./btest -f bitReverse
+        input: ''
+        expected-output: 'Total points: 2/2'
+        comparison-method: contains
+        timeout: 10
+        max-score: 2
     - name: Autograding Reporter
       uses: classroom-resources/autograding-grading-reporter@v1
       env:
@@ -282,5 +295,6 @@ jobs:
         FLOAT_I2F_RESULTS: "${{steps.float_i2f.outputs.result}}"
         ODDPARITY_RESULTS: "${{steps.oddparity.outputs.result}}"
         BITCOUNT_RESULTS: "${{steps.bitcount.outputs.result}}"
+        BITREVERSE_RESULTS: "${{steps.bitreverse.outputs.result}}"
       with:
-        runners: operator-check,signmask,bitxor,clearbyte,roundup,negativepart,islargerorequal,logicalshift,swapnibblepairs,secondlowestzerobit,rotaterightbits,fractions,overflowcalc,mul5sat,float_inv,float_half,float_i2f,oddparity,bitcount
+        runners: operator-check,signmask,bitxor,clearbyte,roundup,negativepart,islargerorequal,logicalshift,swapnibblepairs,secondlowestzerobit,rotaterightbits,fractions,overflowcalc,mul5sat,float_inv,float_half,float_i2f,oddparity,bitcount,bitreverse

bits.c

@@ -631,3 +631,27 @@ int bitCount(int x) {
 
   return x;
 }
+
+// P19
+/*
+ * bitReverse - Reverse bits in an 32-bit integer
+ *   Examples: bitReverse(0x80000004) = 0x20000001
+ *             bitReverse(0x7FFFFFFF) = 0xFFFFFFFE
+ *   Legal ops: ! ~ & ^ | + << >>
+ *   Max ops: 56
+ *   Rating: 2
+ */
+int bitReverse(int x)
+{
+  int m1 = 255 + (255 << 8);
+  int m2 = m1 ^ (m1 << 8);
+  int m3 = m2 ^ (m2 << 4);
+  int m4 = m3 ^ (m3 << 2);
+  int m5 = m4 ^ (m4 << 1);
+  x = ((x >> 16) & m1) + (x << 16);
+  x = ((x & m2) << 8) + ((x >> 8) & m2);
+  x = ((x & m3) << 4) + ((x >> 4) & m3);
+  x = ((x & m4) << 2) + ((x >> 2) & m4);
+  x = ((x & m5) << 1) + ((x >> 1) & m5);
+  return x;
+}

bits.h

@@ -14,6 +14,7 @@ int bitXor(int x, int y);
 int negativePart(int x);
 int isLargerOrEqual(int x, int y);
 int bitCount(int x);
+int bitReverse(int x);
 int logicalShift(int x, int n);
 unsigned float_half(unsigned uf);
 
@@ -34,6 +35,7 @@ int test_signMask(void);
 int test_negativePart(int x);
 int test_isLargerOrEqual(int x, int y);
 int test_bitCount(int x);
+int test_bitReverse(int x);
 int test_logicalShift(int x, int n);
 unsigned test_float_half(unsigned uf);
 int test_mul5Sat(int x);