From 3a96085b999220c4da0c5ef7d1f7ba26b9ddfb98 Mon Sep 17 00:00:00 2001
From: Waldemar Brodkorb <wbx@openadk.org>
Date: Sun, 31 Dec 2017 18:47:16 +0100
Subject: dec-multia: make netboot possible, add aboot bootloader

---
 package/aboot/src/lib/divide.S | 160 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 160 insertions(+)
 create mode 100644 package/aboot/src/lib/divide.S

(limited to 'package/aboot/src/lib/divide.S')

diff --git a/package/aboot/src/lib/divide.S b/package/aboot/src/lib/divide.S
new file mode 100644
index 000000000..36668ab59
--- /dev/null
+++ b/package/aboot/src/lib/divide.S
@@ -0,0 +1,160 @@
+/*
+ * arch/alpha/lib/divide.S
+ *
+ * (C) 1995 Linus Torvalds
+ *
+ * Alpha division..
+ */
+
+/*
+ * The alpha chip doesn't provide hardware division, so we have to do it
+ * by hand.  The compiler expects the functions
+ *
+ *	__divqu: 64-bit unsigned long divide
+ *	__remqu: 64-bit unsigned long remainder
+ *	__divqs/__remqs: signed 64-bit
+ *	__divlu/__remlu: unsigned 32-bit
+ *	__divls/__remls: signed 32-bit
+ *
+ * These are not normal C functions: instead of the normal
+ * calling sequence, these expect their arguments in registers
+ * $24 and $25, and return the result in $27. Register $28 may
+ * be clobbered (assembly temporary), anything else must be saved. 
+ *
+ * In short: painful.
+ *
+ * This is a rather simple bit-at-a-time algorithm: it's very good
+ * at dividing random 64-bit numbers, but the more usual case where
+ * the divisor is small is handled better by the DEC algorithm
+ * using lookup tables. This uses much less memory, though, and is
+ * nicer on the cache.. Besides, I don't know the copyright status
+ * of the DEC code.
+ */
+
+/*
+ * My temporaries:
+ *	$0 - current bit
+ *	$1 - shifted divisor
+ *	$2 - modulus/quotient
+ *
+ *	$23 - return address
+ *	$24 - dividend
+ *	$25 - divisor
+ *
+ *	$27 - quotient/modulus
+ *	$28 - compare status
+ */
+
+#define halt .long 0
+
+/*
+ * Select function type and registers
+ */
+#define mask	$0
+#define divisor	$1
+#define compare $28
+
+#ifdef DIV
+#define func(x) __div##x
+#define modulus $2
+#define quotient $27
+#define GETSIGN(x) xor $24,$25,x
+#else
+#define func(x) __rem##x
+#define modulus $27
+#define quotient $2
+#define GETSIGN(x) bis $24,$24,x
+#endif
+
+/*
+ * For 32-bit operations, we need to extend to 64-bit
+ */
+#ifdef INTSIZE
+#define ufunction func(lu)
+#define sfunction func(l)
+#define LONGIFY(x) zapnot x,15,x
+#define SLONGIFY(x) addl x,0,x
+#else
+#define ufunction func(qu)
+#define sfunction func(q)
+#define LONGIFY(x)
+#define SLONGIFY(x)
+#endif
+
+.set noat
+.globl	ufunction
+.ent	ufunction
+ufunction:
+	subq	$30,32,$30
+	stq	$0, 0($30)
+	stq	$1, 8($30)
+	stq	$2,16($30)
+
+	bis	$25,$25,divisor
+	bis	$24,$24,modulus
+	bis	$31,$31,quotient
+	LONGIFY(divisor)
+	LONGIFY(modulus)
+	beq	divisor, 9f			/* div by zero */
+	bis	$31,1,mask
+
+	/* shift divisor left */
+1:	cmpult	divisor,modulus,compare
+	blt	divisor, 3f
+	addq	divisor,divisor,divisor
+	addq	mask,mask,mask
+	bne	compare,1b
+
+	/* ok, start to go right again.. */
+2:	srl	divisor,1,divisor
+	beq	mask,9f
+	srl	mask,1,mask
+3:	cmpule	divisor,modulus,compare
+	beq	compare,2b
+	addq	quotient,mask,quotient
+	beq	mask,9f
+	subq	modulus,divisor,modulus
+	br	2b
+
+9:	ldq	$0, 0($30)
+	ldq	$1, 8($30)
+	ldq	$2, 16($30)
+	addq	$30,32,$30
+	ret	$31,($23),1
+	.end	ufunction
+
+/*
+ * Uhh.. Ugly signed division. I'd rather not have it at all, but
+ * it's needed in some circumstances. There are different ways to
+ * handle this, really. This does:
+ * 	-a / b = a / -b = -(a / b)
+ *	-a % b = a % b
+ *	a % -b = -(a % b)
+ * which is probably not the best solution, but at least should
+ * have the property that (x/y)*y + (x%y) = x.
+ */
+.globl	sfunction
+.ent	sfunction
+sfunction:
+	bis	$24,$25,$28
+	SLONGIFY($28)
+	bge	$28,ufunction
+	subq	$30,32,$30
+	stq	$23,0($30)
+	stq	$24,8($30)
+	stq	$25,16($30)
+	subq	$31,$24,$28
+	cmovlt	$24,$28,$24	/* abs($24) */
+	subq	$31,$25,$28
+	cmovlt	$25,$28,$25	/* abs($25) */
+	bsr	$23,ufunction
+	ldq	$23,0($30)
+	ldq	$24,8($30)
+	ldq	$25,16($30)
+	addq	$30,32,$30
+	GETSIGN($28)
+	SLONGIFY($28)
+	bge	$28,1f
+	subq	$31,$27,$27
+1:	ret	$31,($23),1
+	.end	sfunction
-- 
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