/*CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
C                                                                             C
C  COMPUTE MERTENS FUNCTION (sum of M(x/i)^2)				      C
C  12/20/14 (DKC)							      C
C                                                                             C
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC*/
#include <math.h>
#include <stdio.h>
unsigned int max=1000; // maximum x value
unsigned int start=2;  // beginning x value, normally set to 2
unsigned int out=1;    // output flag, 0 for M(x), 1 for sum, 2 for histogram
unsigned int bins=100; // number of histogram bins (for out=2)
unsigned int n=1;      // decimation factor (normally set to 1)
unsigned int sflag=0;  // square root flag
unsigned int limit=0;  // partial sum flag (usually set to 0)
void main() {
short m[500000];
int sum,t;
unsigned int i,j,index,hisdif[101],width,flag,savsum,savind,numone;
double delta,newsum,oldsum,maxdel,maxsav[10];
FILE *Outfp;
Outfp = fopen("out7.dat","w");
if (max>500000) {
   printf("x value too large \n");
   goto zskip;
   }
if ((out==2)&&(sflag==0)) {
   printf("parameter error \n");
   goto zskip;
   }
//
// compute Mertens function
//
m[0]=1;
if (out==0) {
// printf(" %d \n",1);
   fprintf(Outfp," %d \n",1);
   }
for (index=2; index<=max; index++) {
   sum=0;
   for (i=2; i<=(index/3); i++)
      sum=sum+m[index/i-1];
   sum=sum+(index+1)/2;
   t=1-sum;
   if ((t>32767)||(t<-32768)) {
      printf("overflow \n");
      goto zskip;
      }
   m[index-1]=(short)t;
   if (out==0) {
//    printf(" %d \n",1-sum);
      fprintf(Outfp," %d \n",1-sum);
      }
   }
if (out==0)
   return;
//
// compute sum or histogram
//
if (out==2) {
   for (i=0; i<101; i++)
      hisdif[i]=0;
   for (i=0; i<10; i++)
      maxsav[i]=0.0;
   numone=0;
   oldsum=0.0;
   maxdel=0.0;
   savsum=0;
   savind=0;
   width=1;
   }
for (index=start; index<=max; index++) {
   sum=0;
   for (i=n; i<=index; i+=n) {
//    if ((index/i)==limit)  // compute d(x) for limit=3, e(x) for limit=4, etc.
//	 printf(" %d %d \n",index,i);
      if ((index/i)<=limit)
	 break;
      sum=sum+(int)m[index/i-1]*(int)m[index/i-1];
      }
   newsum=(double)sum;
   if (sflag!=0)
      newsum=sqrt((double)sum);
   printf(" %d %d \n",index,sum);
   if (out==1)
      fprintf(Outfp," %e\n",newsum);
   else {
      delta=newsum-oldsum;
      flag=0;
      if (delta<0.0) {
	 delta=-delta;
	 flag=1;
	 }
      if (delta>1.0)
	 numone=numone+1;
      if (delta>maxdel) {
	 for (j=9; j>0; j--)
	    maxsav[j]=maxsav[j-1];
	 maxsav[0]=delta;
	 maxdel=delta;
	 savsum=sum;
	 savind=index;
	 }
      oldsum=newsum;
      if (delta>0.00001) {
	 width=width+1;
	 if (width!=(width/n)*n) {
	    printf("error: width=%d \n",width);
	    goto zskip;
	    }
	 width=0;
	 j=(unsigned int)(delta*(double)bins+0.5);
	 if (j<101)
	    hisdif[j]=hisdif[j]+1;
	 }
      else
	 width=width+1;
      }
   }
if (out==2) {
   printf("maximum difference=%e, sum=%d, index=%d \n",maxdel,savsum,savind);
   printf("number greater than one=%d \n",numone);
   for (i=0; i<10; i++)
      printf(" %e \n",maxsav[i]);
   j=0;
   for (i=0; i<=bins; i++) {
      fprintf(Outfp," %d \n",hisdif[i]);
      j=j+hisdif[i];
      }
   printf("sum=%d \n",j);
   }
zskip:
return;
}