quickfactor.cpp

   1 //-----------------------------------------------------------------------------
   2 //
   3 //      Factor small numerical powers
   4 //
   5 //      Input:          tos-2           Base (positive integer < 2^31 - 1)
   6 //
   7 //                      tos-1           Exponent
   8 //
   9 //      Output:         Expr on stack
  10 //
  11 //-----------------------------------------------------------------------------
  12
  13 #include "stdafx.h"
  14 #include "defs.h"
  15
  16 #define BASE p1
  17 #define EXPO p2
  18
  19 static void quickpower(void);
  20
  21 void
  22 quickfactor(void)
  23 {
  24         int h, i, n;
  25         U **s;
  26
  27         save();
  28
  29         EXPO = pop();
  30         BASE = pop();
  31
  32         h = tos;
  33
  34         push(BASE);
  35
  36         factor_small_number();
  37
  38         n = tos - h;
  39
  40         s = stack + h;
  41
  42         for (i = 0; i < n; i += 2) {
  43                 push(s[i]);             // factored base
  44                 push(s[i + 1]);         // factored exponent
  45                 push(EXPO);
  46                 multiply();
  47                 quickpower();
  48         }
  49
  50         // stack has n results from factor_number_raw()
  51
  52         // on top of that are all the expressions from quickpower()
  53
  54         // multiply the quickpower() results
  55
  56         multiply_all(tos - h - n);
  57
  58         p1 = pop();
  59
  60         tos = h;
  61
  62         push(p1);
  63
  64         restore();
  65 }
  66
  67 // BASE is a prime number so power is simpler
  68
  69 static void
  70 quickpower(void)
  71 {
  72         int expo;
  73
  74         save();
  75
  76         EXPO = pop();
  77         BASE = pop();
  78
  79         push(EXPO);
  80         bignum_truncate();
  81         p3 = pop();
  82
  83         push(EXPO);
  84         push(p3);
  85         subtract();
  86         p4 = pop();
  87
  88         // fractional part of EXPO
  89
  90         if (!iszero(p4)) {
  91                 push_symbol(POWER);
  92                 push(BASE);
  93                 push(p4);
  94                 list(3);
  95         }
  96
  97         push(p3);
  98         expo = pop_integer();
  99
 100         if (expo == (int) 0x80000000) {
 101                 push_symbol(POWER);
 102                 push(BASE);
 103                 push(p3);
 104                 list(3);
 105                 restore();
 106                 return;
 107         }
 108
 109         if (expo == 0) {
 110                 restore();
 111                 return;
 112         }
 113
 114         push(BASE);
 115         bignum_power_number(expo);
 116
 117         restore();
 118 }