openpower/sv/biginteger/mulmnu.c

   1 /* from hacker's delight, originsl by hannah suarez (hcs0) */
   2 // Computes the m+n-halfword product of n halfwords x m halfwords, unsigned.
   3 // Max line length is 57, to fit in hacker.book.
   4 #include <stdio.h>
   5 #include <stdlib.h> //To define "exit", req'd by XLC.
   6
   7 // w[0], u[0], and v[0] contain the LEAST significant halfwords.
   8 // (The halfwords are in little-endian order).
   9 // This is Knuth's Algorithm M from [Knuth Vol. 2 Third edition (1998)]
  10 // section 4.3.1.  Picture is:
  11 //                   u[m-1] ... u[1] u[0]
  12 //                 x v[n-1] ... v[1] v[0]
  13 //                   --------------------
  14 //        w[m+n-1] ............ w[1] w[0]
  15
  16 void mulmnu(unsigned short w[], unsigned short u[], unsigned short v[], int m,
  17             int n)
  18 {
  19
  20     unsigned int k, t;
  21     int i, j;
  22
  23     for (i = 0; i < m; i++)
  24         w[i] = 0;
  25
  26     for (j = 0; j < n; j++)
  27     {
  28         k = 0;
  29         unsigned short phi[2000];
  30         unsigned short plo[2000];
  31         for (i = 0; i < m; i++)
  32         {
  33             unsigned product = (unsigned)u[i] * v[j] + w[i + j];
  34             phi[i] = product >> 16;
  35             plo[i] = product;
  36         }
  37         for (i = 0; i < m; i++)
  38         {
  39             t = (((unsigned)phi[i] << 16) | plo[i]) + k;
  40             w[i + j] = t; // (I.e., t & 0xFFFF).
  41             k = t >> 16;
  42         }
  43         w[j + m] = k;
  44     }
  45     return;
  46 }
  47
  48 int errors;
  49
  50 void check(unsigned short result[], unsigned short u[], unsigned short v[],
  51            int m, int n, unsigned short correct[])
  52 {
  53     int i, j;
  54
  55     for (i = 0; i < m + n; i++)
  56     {
  57         if (correct[i] != result[i])
  58         {
  59             errors = errors + 1;
  60             printf("Error, m = %d, n = %d, u = ", m, n);
  61             for (j = 0; j < m; j++)
  62                 printf(" %04x", u[j]);
  63             printf(" v =");
  64             for (j = 0; j < n; j++)
  65                 printf(" %04x", v[j]);
  66             printf("\nShould get:");
  67             for (j = 0; j < n + m; j++)
  68                 printf(" %04x", correct[j]);
  69             printf("\n       Got:");
  70             for (j = 0; j < n + m; j++)
  71                 printf(" %04x", result[j]);
  72             printf("\n");
  73             break;
  74         }
  75     }
  76 }
  77
  78 int main()
  79 {
  80     static struct
  81     {
  82         int m, n;
  83         unsigned short u[4], v[4], correct[8];
  84     } test[] = {
  85         // clang-format off
  86         {.m=1, .n=1, .u={7}, .v={3}, .correct={21, 0}},
  87         {.m=1, .n=1, .u={2}, .v={0xFFFF}, .correct={0xFFFE, 0x0001}}, // 2*FFFF = 0001_FFFE.
  88         {.m=1, .n=1, .u={0xFFFF}, .v={0xFFFF}, .correct={1, 0xFFFE}},
  89         {.m=1, .n=2, .u={7}, .v={5, 6}, .correct={35, 42, 0}},
  90         {.m=1, .n=2, .u={65000}, .v={63000, 64000}, .correct={0xBDC0, 0x8414, 0xF7F5}},
  91         {.m=1, .n=3, .u={65535}, .v={31000, 32000, 33000}, .correct={0x86E8, 0xFC17, 0xFC17, 0x80E7}},
  92         {.m=2, .n=3, .u={400, 300}, .v={500, 100, 200}, .correct={0x0D40, 0xE633, 0xADB2, 0xEA61, 0}},
  93         {.m=2, .n=3, .u={400, 65535}, .v={500, 100, 65534}, .correct={0x0D40, 0x9A4F, 0xFE70, 0x01F5, 0xFFFD}},
  94         {.m=4, .n=4, .u={65535, 65535, 65535, 65535}, .v={65535, 65535, 65535, 65535},
  95          .correct={1, 0, 0, 0, 65534, 65535, 65535, 65535}},
  96         {.m=2, .n=2, .u={0xFF00, 0xFF00}, .v={0xFF00, 0xFF00}, .correct={0, 0xfe01, 0xfc02, 0xfe02}},
  97         // clang-format on
  98     };
  99     const int ncases = sizeof(test) / sizeof(test[0]);
 100     unsigned short result[10];
 101
 102     printf("mulmnu:\n");
 103     for (int i = 0; i < ncases; i++)
 104     {
 105         int m = test[i].m, n = test[i].n;
 106         unsigned short *u = test[i].u;
 107         unsigned short *v = test[i].v;
 108         unsigned short *correct = test[i].correct;
 109         mulmnu(result, u, v, m, n);
 110         check(result, u, v, m, n, correct);
 111         mulmnu(result, v, u, n, m); // Interchange operands.
 112         check(result, v, u, n, m, correct);
 113     }
 114
 115     if (errors == 0)
 116         printf("Passed all %d cases.\n", ncases);
 117 }