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+/*
+ * 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