From: Alan Cox <alan@linux.intel.com>
Date: Sun, 18 Feb 2018 14:01:56 +0000 (+0000)
Subject: pdp11: udivhi3 helper
X-Git-Url: https://git.ndcode.org/public/gitweb.cgi?a=commitdiff_plain;h=fce899c4c7a4c6bf0692edd40b9c0cb089fabed0;p=FUZIX.git

pdp11: udivhi3 helper
---

diff --git a/Library/libs/udivhi3_pdp11.S b/Library/libs/udivhi3_pdp11.S
new file mode 100644
index 00000000..52c05423
--- /dev/null
+++ b/Library/libs/udivhi3_pdp11.S
@@ -0,0 +1,82 @@
+/*
+ *	The PDP 11 have a signed divide (except early machines) but not an
+ *	unsigned one. For some reason the PDP-11 gcc support lib forgets to
+ *	include this helper so we use our own
+ *
+ *	There are faster divide algorithms based upon lookup tables but they
+ *	take a lot more memory.
+ *
+ *	WARNING: untested at this point
+ */
+	.text
+	.even
+
+	.globl ___divmodhi3
+	.globl ___umodhi3
+	.globl ___udivhi3
+/*
+ *	Maybe should panic ?
+ */
+divide_zero:
+	clr r0
+	clr r1
+	rts pc
+
+divops:
+	mov $1,r0
+	clr r1
+	tst r3
+	beq divide_zero
+align:
+	cmp r2,r3
+	bhis divide	/* if its bigger we are done */
+	bmi divide	/* if the top bit is set we are done */
+	tst r0
+	beq divide	/* and if we ran out of bits it is done */
+	asl r0
+	asl r3
+	br align
+divide:
+	tst r0		/* keep going until we've dealt with each bit we
+			   set in the first pass */
+	beq donediv
+	cmp r3,r2
+	blo wentover
+	sub r3,r2	/* set the bit and account for that chunk */
+	bis r0,r1
+wentover:
+	clc
+	ror r0
+	clc
+	ror r3
+	br divide
+donediv:
+	mov r2,r1	/* makes it easier to handle */
+	rts pc
+
+/*
+ *	Basically a C wrapper around the helper that returns the answer
+ *	in r0 and r1.
+ *
+ *	For the later machines I'm not clear if this or somehow mangling div
+ * 	into udiv is faster.
+ */
+___divmodhi3:
+	mov r2,-(sp)
+	mov r3,-(sp)
+	mov 8(sp),r2
+	mov 10(sp),r3
+	jsr pc,divops
+	mov (sp)+,r3
+	mov (sp)+,r2
+	rts pc
+/*
+ *	And we get both forms just by looking at r0 or r1
+ */
+___umodhi3:
+	jsr pc,___divmodhi3
+	mov r1,r0
+	rts pc
+___udivhi3:
+	jsr pc,___divmodhi3
+	rts pc