diff --git a/armsrc/util.c b/armsrc/util.c
index 2fa0683df..7ed190162 100644
--- a/armsrc/util.c
+++ b/armsrc/util.c
@@ -13,6 +13,23 @@ size_t nbytes(size_t nbits) {
 	return (nbits >> 3)+((nbits % 8) > 0);
 }
 
+/*
+ ref  http://www.csm.ornl.gov/~dunigan/crc.html
+ Returns the value v with the bottom b [0,32] bits reflected. 
+ Example: reflect(0x3e23L,3) == 0x3e26
+*/
+uint32_t reflect(uint32_t v, int b) {
+	uint32_t t = v;
+	for ( int i = 0; i < b; ++i) {
+		if (t & 1)
+			v |=  BITMASK((b-1)-i);
+		else
+			v &= ~BITMASK((b-1)-i);
+		t>>=1;
+	}
+	return v;
+}
+
 uint8_t reflect8(uint8_t b) {
 	return ((b * 0x80200802ULL) & 0x0884422110ULL) * 0x0101010101ULL >> 32;
 }
diff --git a/armsrc/util.h b/armsrc/util.h
index 6f9998751..77fd81ee4 100644
--- a/armsrc/util.h
+++ b/armsrc/util.h
@@ -41,6 +41,7 @@
 
 size_t nbytes(size_t nbits);
 
+extern uint32_t reflect(uint32_t v, int b); // used in crc.c ...
 extern uint8_t reflect8(uint8_t b);		// dedicated 8bit reversal
 extern uint16_t reflect16(uint16_t b);	// dedicated 16bit reversal