1 /* original source code from Hackers-Delight
2 https://github.com/hcs0/Hackers-Delight
4 /* This divides an n-word dividend by an m-word divisor, giving an
5 n-m+1-word quotient and m-word remainder. The bignums are in arrays of
6 words. Here a "word" is 32 bits. This routine is designed for a 64-bit
7 machine which has a 64/64 division instruction. */
10 #include <stdlib.h> //To define "exit", req'd by XLC.
12 #define max(x, y) ((x) > (y) ? (x) : (y))
17 if (x
== 0) return(32);
19 if (x
<= 0x0000FFFF) {n
= n
+16; x
= x
<<16;}
20 if (x
<= 0x00FFFFFF) {n
= n
+ 8; x
= x
<< 8;}
21 if (x
<= 0x0FFFFFFF) {n
= n
+ 4; x
= x
<< 4;}
22 if (x
<= 0x3FFFFFFF) {n
= n
+ 2; x
= x
<< 2;}
23 if (x
<= 0x7FFFFFFF) {n
= n
+ 1;}
27 void dumpit(char *msg
, int n
, unsigned v
[]) {
30 for (i
= n
-1; i
>= 0; i
--) printf(" %08x", v
[i
]);
34 /* q[0], r[0], u[0], and v[0] contain the LEAST significant words.
35 (The sequence is in little-endian order).
37 This is a fairly precise implementation of Knuth's Algorithm D, for a
38 binary computer with base b = 2**32. The caller supplies:
39 1. Space q for the quotient, m - n + 1 words (at least one).
40 2. Space r for the remainder (optional), n words.
41 3. The dividend u, m words, m >= 1.
42 4. The divisor v, n words, n >= 2.
43 The most significant digit of the divisor, v[n-1], must be nonzero. The
44 dividend u may have leading zeros; this just makes the algorithm take
45 longer and makes the quotient contain more leading zeros. A value of
46 NULL may be given for the address of the remainder to signify that the
47 caller does not want the remainder.
48 The program does not alter the input parameters u and v.
49 The quotient and remainder returned may have leading zeros. The
50 function itself returns a value of 0 for success and 1 for invalid
51 parameters (e.g., division by 0).
52 For now, we must have m >= n. Knuth's Algorithm D also requires
53 that the dividend be at least as long as the divisor. (In his terms,
54 m >= 0 (unstated). Therefore m+n >= n.) */
56 int divmnu(unsigned q
[], unsigned r
[],
57 const unsigned u
[], const unsigned v
[],
60 const unsigned long long b
= 4294967296LL; // Number base (2**32).
61 unsigned *un
, *vn
; // Normalized form of u, v.
62 unsigned long long qhat
; // Estimated quotient digit.
63 unsigned long long rhat
; // A remainder.
64 unsigned long long p
; // Product of two digits.
68 if (m
< n
|| n
<= 0 || v
[n
-1] == 0)
69 return 1; // Return if invalid param.
71 if (n
== 1) { // Take care of
72 k
= 0; // the case of a
73 for (j
= m
- 1; j
>= 0; j
--) { // single-digit
74 q
[j
] = (k
*b
+ u
[j
])/v
[0]; // divisor here.
75 k
= (k
*b
+ u
[j
]) - q
[j
]*v
[0];
77 if (r
!= NULL
) r
[0] = k
;
81 /* Normalize by shifting v left just enough so that its high-order
82 bit is on, and shift u left the same amount. We may have to append a
83 high-order digit on the dividend; we do that unconditionally. */
85 s
= nlz(v
[n
-1]); // 0 <= s <= 31.
86 vn
= (unsigned *)alloca(4*n
);
87 for (i
= n
- 1; i
> 0; i
--)
88 vn
[i
] = (v
[i
] << s
) | ((unsigned long long)v
[i
-1] >> (32-s
));
91 un
= (unsigned *)alloca(4*(m
+ 1));
92 un
[m
] = (unsigned long long)u
[m
-1] >> (32-s
);
93 for (i
= m
- 1; i
> 0; i
--)
94 un
[i
] = (u
[i
] << s
) | ((unsigned long long)u
[i
-1] >> (32-s
));
97 for (j
= m
- n
; j
>= 0; j
--) { // Main loop.
98 // Compute estimate qhat of q[j].
99 qhat
= (un
[j
+n
]*b
+ un
[j
+n
-1])/vn
[n
-1];
100 rhat
= (un
[j
+n
]*b
+ un
[j
+n
-1]) - qhat
*vn
[n
-1];
102 if (qhat
>= b
|| qhat
*vn
[n
-2] > b
*rhat
+ un
[j
+n
-2])
104 rhat
= rhat
+ vn
[n
-1];
105 if (rhat
< b
) goto again
;
108 // Multiply and subtract.
110 for (i
= 0; i
< n
; i
++) {
112 t
= un
[i
+j
] - k
- (p
& 0xFFFFFFFFLL
);
114 k
= (p
>> 32) - (t
>> 32);
119 q
[j
] = qhat
; // Store quotient digit.
120 if (t
< 0) { // If we subtracted too
121 q
[j
] = q
[j
] - 1; // much, add back.
123 for (i
= 0; i
< n
; i
++) {
124 t
= (unsigned long long)un
[i
+j
] + vn
[i
] + k
;
128 un
[j
+n
] = un
[j
+n
] + k
;
131 // If the caller wants the remainder, unnormalize
132 // it and pass it back.
134 for (i
= 0; i
< n
-1; i
++)
135 r
[i
] = (un
[i
] >> s
) | ((unsigned long long)un
[i
+1] << (32-s
));
136 r
[n
-1] = un
[n
-1] >> s
;
143 void check(unsigned q
[], unsigned r
[],
144 unsigned u
[], unsigned v
[],
146 unsigned cq
[], unsigned cr
[]) {
149 szq
= max(m
- n
+ 1, 1);
150 for (i
= 0; i
< szq
; i
++) {
153 dumpit("Error, dividend u =", m
, u
);
154 dumpit(" divisor v =", n
, v
);
155 dumpit("For quotient, got:", m
-n
+1, q
);
156 dumpit(" Should get:", m
-n
+1, cq
);
160 for (i
= 0; i
< n
; i
++) {
163 dumpit("Error, dividend u =", m
, u
);
164 dumpit(" divisor v =", n
, v
);
165 dumpit("For remainder, got:", n
, r
);
166 dumpit(" Should get:", n
, cr
);
174 static unsigned test
[] = {
175 // m, n, u..., v..., cq..., cr....
176 1, 1, 3, 0, 1, 1, // Error, divide by 0.
177 1, 2, 7, 1,3, 0, 7,0, // Error, n > m.
178 2, 2, 0,0, 1,0, 0, 0,0, // Error, incorrect remainder cr.
182 1, 1, 0, 0xffffffff, 0, 0,
183 1, 1, 0xffffffff, 1, 0xffffffff, 0,
184 1, 1, 0xffffffff, 0xffffffff, 1, 0,
185 1, 1, 0xffffffff, 3, 0x55555555, 0,
186 2, 1, 0xffffffff,0xffffffff, 1, 0xffffffff,0xffffffff, 0,
187 2, 1, 0xffffffff,0xffffffff, 0xffffffff, 1,1, 0,
188 2, 1, 0xffffffff,0xfffffffe, 0xffffffff, 0xffffffff,0, 0xfffffffe,
189 2, 1, 0x00005678,0x00001234, 0x00009abc, 0x1e1dba76,0, 0x6bd0,
190 2, 2, 0,0, 0,1, 0, 0,0,
191 2, 2, 0,7, 0,3, 2, 0,1,
192 2, 2, 5,7, 0,3, 2, 5,1,
193 2, 2, 0,6, 0,2, 3, 0,0,
194 1, 1, 0x80000000, 0x40000001, 0x00000001, 0x3fffffff,
195 2, 1, 0x00000000,0x80000000, 0x40000001, 0xfffffff8,0x00000001, 0x00000008,
196 2, 2, 0x00000000,0x80000000, 0x00000001,0x40000000, 0x00000001, 0xffffffff,0x3fffffff,
197 2, 2, 0x0000789a,0x0000bcde, 0x0000789a,0x0000bcde, 1, 0,0,
198 2, 2, 0x0000789b,0x0000bcde, 0x0000789a,0x0000bcde, 1, 1,0,
199 2, 2, 0x00007899,0x0000bcde, 0x0000789a,0x0000bcde, 0, 0x00007899,0x0000bcde,
200 2, 2, 0x0000ffff,0x0000ffff, 0x0000ffff,0x0000ffff, 1, 0,0,
201 2, 2, 0x0000ffff,0x0000ffff, 0x00000000,0x00000001, 0x0000ffff, 0x0000ffff,0,
202 3, 2, 0x000089ab,0x00004567,0x00000123, 0x00000000,0x00000001, 0x00004567,0x00000123, 0x000089ab,0,
203 3, 2, 0x00000000,0x0000fffe,0x00008000, 0x0000ffff,0x00008000, 0xffffffff,0x00000000, 0x0000ffff,0x00007fff, // Shows that first qhat can = b + 1.
204 3, 3, 0x00000003,0x00000000,0x80000000, 0x00000001,0x00000000,0x20000000, 0x00000003, 0,0,0x20000000, // Adding back step req'd.
205 3, 3, 0x00000003,0x00000000,0x00008000, 0x00000001,0x00000000,0x00002000, 0x00000003, 0,0,0x00002000, // Adding back step req'd.
206 4, 3, 0,0,0x00008000,0x00007fff, 1,0,0x00008000, 0xfffe0000,0, 0x00020000,0xffffffff,0x00007fff, // Add back req'd.
207 4, 3, 0,0x0000fffe,0,0x00008000, 0x0000ffff,0,0x00008000, 0xffffffff,0, 0x0000ffff,0xffffffff,0x00007fff, // Shows that mult-sub quantity cannot be treated as signed.
208 4, 3, 0,0xfffffffe,0,0x80000000, 0x0000ffff,0,0x80000000, 0x00000000,1, 0x00000000,0xfffeffff,0x00000000, // Shows that mult-sub quantity cannot be treated as signed.
209 4, 3, 0,0xfffffffe,0,0x80000000, 0xffffffff,0,0x80000000, 0xffffffff,0, 0xffffffff,0xffffffff,0x7fffffff, // Shows that mult-sub quantity cannot be treated as signed.
211 int i
, n
, m
, ncases
, f
;
212 unsigned q
[10], r
[10];
213 unsigned *u
, *v
, *cq
, *cr
;
218 while (i
< sizeof(test
)/4) {
224 cr
= &test
[i
+2+m
+n
+max(m
-n
+1, 1)];
226 f
= divmnu(q
, r
, u
, v
, m
, n
);
228 dumpit("Error return code for dividend u =", m
, u
);
229 dumpit(" divisor v =", n
, v
);
233 check(q
, r
, u
, v
, m
, n
, cq
, cr
);
234 i
= i
+ 2 + m
+ n
+ max(m
-n
+1, 1) + n
;
238 printf("%d errors out of %d cases; there should be 3.\n", errors
, ncases
);