tmpdigdiv.c - plan9port - [fork] Plan 9 from user space
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       ---
       tmpdigdiv.c (750B)
       ---
            1 #include "os.h"
            2 #include <mp.h>
            3 #include "dat.h"
            4 
            5 /* */
            6 /*        divide two digits by one and return quotient */
            7 /* */
            8 void
            9 mpdigdiv(mpdigit *dividend, mpdigit divisor, mpdigit *quotient)
           10 {
           11         mpdigit hi, lo, q, x, y;
           12         int i;
           13 
           14         hi = dividend[1];
           15         lo = dividend[0];
           16 
           17         /* return highest digit value if the result >= 2**32 */
           18         if(hi >= divisor || divisor == 0){
           19                 divisor = 0;
           20                 *quotient = ~divisor;
           21                 return;
           22         }
           23 
           24         /* at this point we know that hi < divisor */
           25         /* just shift and subtract till we're done */
           26         q = 0;
           27         x = divisor;
           28         for(i = Dbits-1; hi > 0 && i >= 0; i--){
           29                 x >>= 1;
           30                 if(x > hi)
           31                         continue;
           32                 y = divisor<<i;
           33                 if(x == hi && y > lo)
           34                         continue;
           35                 if(y > lo)
           36                         hi--;
           37                 lo -= y;
           38                 hi -= x;
           39                 q |= 1<<i;
           40         }
           41         q += lo/divisor;
           42         *quotient = q;
           43 }