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diff --git a/unix/as.vax/bitfields.s b/unix/as.vax/bitfields.s
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+# BITFIELDS -- Routines for inserting and extracting bitfields into integers.
+
+# BITPAK -- Pack an integer into a bitfield of an array.  Set all nbits
+# bits regardless of the value of the integer.
+
+	.text
+	.align	1
+	.globl	_bitpak_
+
+	# bitpak (intval, array, offset, nbits)
+	.set	INTVAL,	4
+	.set	ARRAY,	8
+	.set	OFFSET,	12		# one-indexed bit offset
+	.set	NBITS,	16
+
+_bitpak_:
+	.word	0x0
+
+	subl3	$1, *OFFSET(ap), r1
+	insv	*INTVAL(ap), r1, *NBITS(ap), *ARRAY(ap)
+	ret
+	.data
+
+# BITUPK -- Unpack a bitfield from an array and return as the function
+# value, an integer.  Do not sign extend.
+
+	.text
+	.align	1
+	.globl	_bitupk_
+
+	# bitupk (array, offset, nbits)
+	.set	ARRAY,	4
+	.set	OFFSET,	8			# one-indexed bit offset
+	.set	NBITS,	12
+
+_bitupk_:
+	.word	0x0
+
+	subl3	$1, *OFFSET(ap), r1
+	extzv	r1, *NBITS(ap), *ARRAY(ap), r0
+	ret
+	.data