Data commit

Task/Bitwise-operations/Python/bitwise-operations-1.py

@@ -0,0 +1,109 @@
+def bitwise_built_ins(width, a, b):
+    mask = (1 << width) - 1
+    print(f"""\
+    AND:     0b{a :0{width}b}
+           & 0b{b :0{width}b}
+           = 0b{(a & b) & mask :0{width}b}
+
+    OR:      0b{a :0{width}b}
+           | 0b{b :0{width}b}
+           = 0b{(a | b) & mask :0{width}b}
+
+    XOR:     0b{a :0{width}b}
+           ^ 0b{b :0{width}b}
+           = 0b{(a ^ b) & mask :0{width}b}
+
+    NOT:   ~ 0b{a :0{width}b}
+           = 0b{(~a) & mask :0{width}b}
+
+    SHIFTS
+
+      RIGHT:   0b{a :0{width}b} >> 1
+             = 0b{(a >> 1) & mask :0{width}b}
+
+      LEFT:    0b{a :0{width}b} << 1
+             = 0b{(a << 1) & mask :0{width}b}
+""")
+
+def rotr(width, a, n):
+    "Rotate a, n times to the right"
+    if n < 0:
+        return rotl(width, a, -n)
+    elif n == 0:
+        return a
+    else:
+        mask = (1 << width) - 1
+        a, n = a & mask, n % width
+        return ((a >> n)    # top moved down
+                | ((a & ((1 << n) - 1))   # Bottom masked...
+                   << (width - n)))  # ... then moved up
+
+def rotl(width, a, n):
+    "Rotate a, n times to the left"
+    if n < 0:
+        return rotr(width, a, -n)
+    elif n == 0:
+        return a
+    else:
+        mask = (1 << width) - 1
+        a, n = a & mask, n % width
+        return (((a << n) & mask)      # bottom shifted up and masked
+                | (a >> (width - n)))  # Top moved down
+
+def asr(width, a, n):
+    "Arithmetic shift a, n times to the right. (sign preserving)."
+    mask, top_bit_mask = ((1 << width) - 1), 1 << (width - 1)
+    if n < 0:
+        return  (a << -n) & mask
+    elif n == 0:
+        return a
+    elif n >= width:
+        return mask if a & top_bit_mask else 0
+    else:
+        a = a & mask
+        if a & top_bit_mask:    # Sign bit set?
+            signs = (1 << n) - 1
+            return a >> n | (signs << width - n)
+        else:
+            return a >> n
+
+
+def helper_funcs(width, a):
+    mask, top_bit_mask = ((1 << width) - 1), 1 << (width - 1)
+    aa = a | top_bit_mask  # a with top bit set
+    print(f"""\
+    ROTATIONS
+
+      RIGHT:   rotr({width}, 0b{a :0{width}b}, 1)
+               =       0b{rotr(width, a, 1) :0{width}b}
+               rotr({width}, 0b{a :0{width}b}, 2)
+               =       0b{rotr(width, a, 2) :0{width}b}
+               rotr({width}, 0b{a :0{width}b}, 4)
+               =       0b{rotr(width, a, 4) :0{width}b}
+
+      LEFT:    rotl({width}, 0b{a :0{width}b}, 1)
+               =       0b{rotl(width, a, 1) :0{width}b}
+               rotl({width}, 0b{a :0{width}b}, 2)
+               =       0b{rotl(width, a, 2) :0{width}b}
+               rotl({width}, 0b{a :0{width}b}, 4)
+               =       0b{rotl(width, a, 4) :0{width}b}
+
+    SIGN-EXTENDING ARITHMETIC SHIFT RIGHT
+
+               asr({width}, 0b{a :0{width}b}, 1)
+               =      0b{asr(width, a, 1) :0{width}b}
+               asr({width}, 0b{aa :0{width}b}, 1)
+               =      0b{asr(width, aa, 1) :0{width}b}
+               asr({width}, 0b{a :0{width}b}, 2)
+               =      0b{asr(width, a, 2) :0{width}b}
+               asr({width}, 0b{aa :0{width}b}, 2)
+               =      0b{asr(width, aa, 2) :0{width}b}
+               asr({width}, 0b{a :0{width}b}, 4)
+               =      0b{asr(width, a, 4) :0{width}b}
+               asr({width}, 0b{aa :0{width}b}, 4)
+               =      0b{asr(width, aa, 4) :0{width}b}
+""")
+
+if __name__ == '__main__':
+    bitwise_built_ins(8, 27, 125)
+    helper_funcs(8, 27)

Task/Bitwise-operations/Python/bitwise-operations-2.py

@@ -0,0 +1,7 @@
+def bitwise(a, b):
+        print 'a and b:', a & b
+        print 'a or b:', a | b
+        print 'a xor b:', a ^ b
+        print 'not a:', ~a
+        print 'a << b:', a << b # left shift
+        print 'a >> b:', a >> b # arithmetic right shift

Task/Bitwise-operations/Python/bitwise-operations-3.py

@@ -0,0 +1,8 @@
+# 8-bit bounded shift:
+x = x << n & 0xff
+# ditto for 16 bit:
+x = x << n & 0xffff
+# ... and 32-bit:
+x = x << n & 0xffffffff
+# ... and 64-bit:
+x = x << n & 0xffffffffffffffff

Task/Bitwise-operations/Python/bitwise-operations-4.py

@@ -0,0 +1,41 @@
+def bitstr(n, width=None):
+   """return the binary representation of n as a string and
+      optionally zero-fill (pad) it to a given length
+   """
+   result = list()
+   while n:
+      result.append(str(n%2))
+      n = int(n/2)
+   if (width is not None) and len(result) < width:
+      result.extend(['0'] * (width - len(result)))
+   result.reverse()
+   return ''.join(result)
+
+def mask(n):
+   """Return a bitmask of length n (suitable for masking against an
+      int to coerce the size to a given length)
+   """
+   if n >= 0:
+       return 2**n - 1
+   else:
+       return 0
+
+def rol(n, rotations=1, width=8):
+    """Return a given number of bitwise left rotations of an integer n,
+       for a given bit field width.
+    """
+    rotations %= width
+    if rotations < 1:
+        return n
+    n &= mask(width) ## Should it be an error to truncate here?
+    return ((n << rotations) & mask(width)) | (n >> (width - rotations))
+
+def ror(n, rotations=1, width=8):
+    """Return a given number of bitwise right rotations of an integer n,
+       for a given bit field width.
+    """
+    rotations %= width
+    if rotations < 1:
+        return n
+    n &= mask(width)
+    return (n >> rotations) | ((n << (width - rotations)) & mask(width))