/*

convert6432.c

Program to modify the header in grd type 1 GMT files 
If these files are generated in Linux, the size of the header is 892;
if they are created in Cygwin or by the Microsoft C binaries, the size
is 896.
This program modifies the header, thus converting files from one
implementation to the other.
>From Linux to Cygwin, it inserts 4 bytes in the header
>From Cygwin to Linux, it removes 4 bytes in the header
The original file is not modified; a new converted file is created.

convert6432 <input grd=1 file> <output grd=1 file> ishift

ishift = 4 to add 4 bytes  (linux to cygwin)
ishift = -4 to remove 4 bytes (cygwin to linux)

Marta, August 3, 2003

mghidella@dna.gov.ar

*/


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <conio.h>
#include <io.h>

main (argc,argv)
int argc;
char **argv; 


{
char *infile, *outfile, *bufch, chaux[4];
FILE *fpin,*fpout;

/* Note that NMAX can be larger; it has to be greater than or equal to the
   grid size in bytes */

  int num,ie,imem,NMAX=4000000, iread,iw,i;
  int nx,ny,node_offset,ishift,npad=0,*pnx;
  float *grid;


  if (argc != 4) { 
      fprintf(stderr,"Needed argumets:\n");
      fprintf(stderr,"1) Input grd file  (grd format =1)\n"); 
      fprintf(stderr,"2) Output grd file (grd format =1)\n"); 
      fprintf(stderr,"3) Number of bytes to shift in the header:\n"); 
      fprintf(stderr,"   4 (adds    4 bytes, linux to cygwin conversion)\n"); 
      fprintf(stderr,"  -4 (removes 4 bytes, cygwin to linux conversion)\n"); 
    exit(-1);
    }

    infile=argv[1]; outfile=argv[2];
    ishift=atoi(argv[3]);
    printf("infile: %s; outfile: %s; shift= %d\n",infile,outfile,ishift);

    if (ishift != 4 && ishift != -4) {
        fprintf(stderr,"third argument has to be either 4 or -4;\n exits ...\n");
        exit(-1);
    }

     if(fpin=fopen(infile,"rb"))
     fprintf(stderr, "opened file: %s \n", infile);
     else {fprintf(stderr, "error opening: %s \n", infile);exit(-1);}

     if(fpout=fopen(outfile,"wb"))
     fprintf(stderr, "opened file: %s \n", outfile);
     else {fprintf(stderr, "error opening: %s \n", outfile);exit(-1);}

/*  Reads the first 4 bytes in the file to check that it is not a netcdf file */

     fread(chaux,1,4,fpin);

     if (chaux[0]==67 && chaux[1]==68 && chaux[2]==70 && chaux[3]==1) {
         fprintf(stderr, "seems to be a netcdf file: chaux= %s \nexits...\n",chaux);
     exit(-1);
     }

/* gets nx from auxiliary char */     
     pnx = (int *) chaux;
     nx=*pnx;

/* Reads ny and node_offset */

     fread(&ny,4,1,fpin);
     fread(&node_offset,4,1,fpin);

/* writes ny, ny and node_offset in the output file */

     fwrite(&nx,4,1,fpout);
     fwrite(&ny,4,1,fpout);
     fwrite(&node_offset,4,1,fpout);

     printf("nx= %d; ny= %d, node_offset=%d\n",nx,ny,node_offset);

/* num is the numbr of grid elements */
     num=nx*ny;

/* only reads in this case */

         if(ishift == -4) {fread(&npad,4,1,fpin);
         }

/* only writes in this case */

         if(ishift ==  4) {fwrite(&npad,4,1,fpout);
         }

     printf("num= %d,num; npad= %d\n",num,npad);

/* calculates number of bytes needed for storage */

     imem=sizeof(float)*num;

/* checks memory */

     if(imem > NMAX) {
         fprintf(stderr,"needed memory greater than expected ...");
         exit(-1);
     }

     else 
     
     fprintf(stderr,"imem= %d\n",imem);
/* allocates memory for the remainder of the header */
     
     bufch=(char *) malloc(880);

/* allocates grid memory  */

     grid=(float *) malloc(imem);
     
/* reads and writes the rest of the header */

     iread=fread(bufch,1,880,fpin);
     iw=fwrite(bufch,1,880,fpout);

     printf("iread= %d iw= %d\n",iread,iw);

/* reads the whole grid */

     iread=fread(grid,4,num,fpin);

/* checks for errors */

     if( iread != num ) {
         fprintf(stderr,"conversion failed; exits ...\n");
         exit(-1);
     }

/* writes the entire grid */

     iw=fwrite(grid,4,num,fpout); 
     
     printf("iread= %d iw= %d\n",iread,iw);

     free(grid);
     free(bufch);
     fclose(fpin);
     fclose(fpout);
}