projects / unix-history / blame
| Commit | Line | Data |
|---|---|---|
| 15637ed4 RG |
1 | #include "longlong.h" |
| 2 | ||
| 3 | static void bmul (); | |
| 4 | ||
| 5 | long long | |
| 6 | __muldi3 (u, v) | |
| 7 | long long u, v; | |
| 8 | { | |
| 9 | long a[2], b[2], c[2][2]; | |
| 10 | long_long w; | |
| 11 | long_long uu, vv; | |
| 12 | ||
| 13 | uu.ll = u; | |
| 14 | vv.ll = v; | |
| 15 | ||
| 16 | a[HIGH] = uu.s.high; | |
| 17 | a[LOW] = uu.s.low; | |
| 18 | b[HIGH] = vv.s.high; | |
| 19 | b[LOW] = vv.s.low; | |
| 20 | ||
| 21 | bmul (a, b, c, sizeof a, sizeof b); | |
| 22 | ||
| 23 | w.s.high = c[LOW][HIGH]; | |
| 24 | w.s.low = c[LOW][LOW]; | |
| 25 | return w.ll; | |
| 26 | } | |
| 27 | ||
| 28 | static void | |
| 29 | bmul (a, b, c, m, n) | |
| 30 | unsigned short *a, *b, *c; | |
| 31 | size_t m, n; | |
| 32 | { | |
| 33 | int i, j; | |
| 34 | unsigned long acc; | |
| 35 | ||
| 36 | bzero (c, m + n); | |
| 37 | ||
| 38 | m /= sizeof *a; | |
| 39 | n /= sizeof *b; | |
| 40 | ||
| 41 | for (j = little_end (n); is_not_msd (j, n); j = next_msd (j)) | |
| 42 | { | |
| 43 | unsigned short *c1 = c + j + little_end (2); | |
| 44 | acc = 0; | |
| 45 | for (i = little_end (m); is_not_msd (i, m); i = next_msd (i)) | |
| 46 | { | |
| 47 | /* Widen before arithmetic to avoid loss of high bits. */ | |
| 48 | acc += (unsigned long) a[i] * b[j] + c1[i]; | |
| 49 | c1[i] = acc & low16; | |
| 50 | acc = acc >> 16; | |
| 51 | } | |
| 52 | c1[i] = acc; | |
| 53 | } | |
| 54 | } |