| 1 | /* |
| 2 | * $Header: mulbig.c,v 1.2 83/11/26 12:13:29 sklower Exp $ |
| 3 | * $Locker: $ |
| 4 | * |
| 5 | * Copyright (c) 1982, Regents, University of California |
| 6 | * |
| 7 | */ |
| 8 | |
| 9 | #include "global.h" |
| 10 | |
| 11 | struct s_dot { long I; struct s_dot *CDR; }; |
| 12 | struct vl { long high; long low; }; |
| 13 | |
| 14 | struct s_dot *mulbig(a,b) |
| 15 | struct s_dot *a, *b; |
| 16 | { |
| 17 | int la = 1, lb = 1; |
| 18 | long *sa, *sb, *sc, *base, *alloca(); |
| 19 | struct s_dot *export(); |
| 20 | register struct s_dot *p; |
| 21 | register int *q, *r, *s; |
| 22 | long carry = 0, test; |
| 23 | struct vl work; |
| 24 | Keepxs(); |
| 25 | |
| 26 | /* compute lengths */ |
| 27 | |
| 28 | for(p = a; p->CDR; p = p->CDR) la++; |
| 29 | for(p = b; p->CDR; p = p->CDR) lb++; |
| 30 | |
| 31 | /* allocate storage areas on the stack */ |
| 32 | |
| 33 | base = alloca((la + la + lb + lb + 1)*sizeof(long)); |
| 34 | sc = base + la + lb + 1; |
| 35 | sb = sc + lb; |
| 36 | sa = sb + la; |
| 37 | q = sa; |
| 38 | |
| 39 | /* copy s_dots onto stack */ |
| 40 | p = a; |
| 41 | do { *--q = p->I; p = p->CDR; } while (p); |
| 42 | p = b; |
| 43 | do { *--q = p->I; p = p->CDR; } while (p); |
| 44 | while(q > base) *--q = 0; /* initialize target */ |
| 45 | |
| 46 | /* perform the multiplication */ |
| 47 | for(q = sb; q > sc; *--s = carry) |
| 48 | for((r = sa, s = (q--) - lb, carry = 0); r > sb;) |
| 49 | { |
| 50 | carry += *--s; |
| 51 | emul(*q,*--r,carry,&work); |
| 52 | test = work.low; |
| 53 | carry = work.high << 2; |
| 54 | if(test < 0) carry += 2; |
| 55 | if(test & 0x40000000) carry +=1; |
| 56 | *s = test & 0x3fffffff; |
| 57 | } |
| 58 | |
| 59 | p = export(sc,base); |
| 60 | Freexs(); |
| 61 | return(p); |
| 62 | } |