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/* unitelogs and unitelns, for MathXpert by M. Beeson */
/*
Original date 2.12.94
5.26.95 code last modified
2.27.98 TRIGCALC_DLL etc.
5.6.13 added include trig.h  and specified return type of two functions where it was missing.
*/

#include <string.h>
#include <assert.h>

#include "globals.h"
#include "ops.h"
#include "order.h"
#include "operator.h"
#include "probtype.h"
#include "algaux.h"
#include "eqn.h"
#include "prover.h"
#include "autosub.h"
#include "symbols.h"
#include "psubst.h"
#include "trig.h"

static int unitelogs_aux(unsigned f, int flag, term t, term *next, char *reason);
/*__________________________________________________________________*/
int unitelogs(term t, term arg, term *next, char *reason)
/* use logofpower in an equation if afterwards it makes all logs have
the same argument. */
{ return unitelogs_aux(LOG,1,t,next,reason);
}
/*__________________________________________________________________*/
int unitelns(term t, term arg, term *next, char *reason)
/* use lnofpower in an equation if afterwards it makes all lns have
the same argument. */

{ return unitelogs_aux(LN,1,t,next,reason);
}
/*__________________________________________________________________*/
int unitelogs2(term t, term arg, term *next, char *reason)
/* use logofproduct in an equation if afterwards it makes all logs have
the same argument. */
{ return unitelogs_aux(LOG,2,t,next,reason);
}
/*__________________________________________________________________*/
int unitelns2(term t, term arg, term *next, char *reason)
/* use lnofproduct in an equation if afterwards it makes all lns have
the same argument. */
{ return unitelogs_aux(LN,2,t,next,reason);
}
/*__________________________________________________________________*/
static int log_power_subterm(term t, term *ans)
/* look for a subterm of t of the form ln u^n or log u^n, with u not constant;
return 0 for success,  1 for failure.  Put the found term in *ans. */
{ int err;
  unsigned short i,n;
  if(ATOMIC(t))
     return 1;
  if(FUNCTOR(t) == LOG || FUNCTOR(t) == LN)
     { if(FUNCTOR(ARG(0,t)) != '^'  || econstant(ARG(0,t)))
          return 1;
       *ans = t;
       return 0;
     }
  n = ARITY(t);
  for(i=0;i<n;i++)
     { err = log_power_subterm(ARG(i,t),ans);
       if(!err)
          return 0;
     }
  return 1;
}
/*__________________________________________________________________*/
static int log_product_subterm(term t, term *ans)
/* look for a subterm of t of the form ln uv or log uv, with uv not constant;
return 0 for success,  1 for failure.  Put the found term in *ans. */
{ int err;
  unsigned short i,n;
  if(ATOMIC(t))
     return 1;
  if(FUNCTOR(t) == LOG || FUNCTOR(t) == LN)
     { if(FUNCTOR(ARG(0,t)) != '*'  || econstant(ARG(0,t)))
          return 1;
       *ans = t;
       return 0;
     }
  n = ARITY(t);
  for(i=0;i<n;i++)
     { err = log_product_subterm(ARG(i,t),ans);
       if(!err)
          return 0;
     }
  return 1;
}

/*__________________________________________________________________*/
static int unitelogs_aux(unsigned f, int flag, term t, term *next, char *reason)
/* do the work of unitelns or unitelogs; f will be LN or LOG */
{ term n,c,s,p,u,temp;
  int err,rval;
  if(FUNCTOR(t) != '=')
     return 1;
  switch(flag)
     { case 1:
          err = log_power_subterm(t,&p);
          break;
       case 2:
          err = log_product_subterm(t,&p);
          break;
       default: assert(0);
     }
  if(err)
     return 1;
  if(FUNCTOR(p) != f)
     return 1;
  u = ARG(0,p);
  if(FUNCTOR(u) == '^' && econstant(ARG(1,u)))
     p = f==LN ? ln1(ARG(0,u)) : log1(ARG(0,u));
     /* Not  ARGREP(p,0,ARG(0,u)) which trashes t, as the args of p
        are still part of t; only the head of p is local. */
  else if(FUNCTOR(u) == '*')
     { ncs(u,&n,&c,&s);
       p = f==LN ? ln1(s) : log1(s);
     }
  /* In case p was ln x^n or ln(ax^n) it is now ln x */
  SETCOLOR(p,YELLOW);   /* this colors only the ln term itself, but
                           the only alternative would be to color the
                           entire answer. */
  rval = psubst(var0,p,t,&temp);
  if(rval != 3)
     return 1;
  if(!econstant(temp))
     return 1;   /* the eigenvariable was not eliminated */
  subst(p,var0,temp,next);
  if(FUNCTOR(p) == LN && flag==1)
     strcpy(reason, english(1138));
          /* ln a^n = n ln a */
  else if(FUNCTOR(p) == LOG && flag==1)
     strcpy(reason, english(1140));
          /* log a^n = n log a */
  else if(FUNCTOR(p) == LN)
     strcpy(reason, "ln ab = ln a + ln b");
  else
     strcpy(reason, "log ab=log a + log b");
  return 0;
}