Python Bit Reversal code added.

README.md

@@ -107,7 +107,8 @@ data in a manner which ensures data integrity.
 Access the simpler of the Pyboard's watchdog timers.
 
 # reverse
-Fast reverse a bytearray.
+Fast reverse a bytearray in Arm Thumb assembler.  
+Python code to bit-reverse (fast-ish) 8, 16 and 32 bit words.
 
 # ds3231_pb
 Driver for the DS3231 low cost precison RTC, including a facility to calibrate the Pyboard's RTC

reverse/reverse.py

@@ -11,7 +11,7 @@ def reverse(r0, r1):               # bytearray, len(bytearray)
     sub(r4, 1)
     cmp(r4, r0)
     bpl(LOOP)
-   
+
 def test():
     a = bytearray([0, 1, 2, 3]) # even length
     reverse(a, len(a))
@@ -19,5 +19,25 @@ def test():
     a = bytearray([0, 1, 2, 3, 4]) # odd length
     reverse(a, len(a))
     print(a)
-    
 
+
+# Bit reverse an 8 bit value
+def rbit8(v):
+    v = (v & 0x0f) << 4 | (v & 0xf0) >> 4
+    v = (v & 0x33) << 2 | (v & 0xcc) >> 2
+    return (v & 0x55) << 1 | (v & 0xaa) >> 1
+
+# Bit reverse a 16 bit value
+def rbit16(v):
+    v = (v & 0x00ff) << 8 | (v & 0xff00) >> 8
+    v = (v & 0x0f0f) << 4 | (v & 0xf0f0) >> 4
+    v = (v & 0x3333) << 2 | (v & 0xcccc) >> 2
+    return (v & 0x5555) << 1 | (v & 0xaaaa) >> 1
+
+# Bit reverse a 32 bit value
+def rbit32(v):
+    v = (v & 0x0000ffff) << 16 | (v & 0xffff0000) >> 16
+    v = (v & 0x00ff00ff) << 8 | (v & 0xff00ff00) >> 8
+    v = (v & 0x0f0f0f0f) << 4 | (v & 0xf0f0f0f0) >> 4
+    v = (v & 0x33333333) << 2 | (v & 0xcccccccc) >> 2
+    return (v & 0x55555555) << 1 | (v & 0xaaaaaaaa) >> 1