Huffman encoding (old OJ question)

huffman.c

#include <stdio.h>

int charrate[128] = {0};
typedef struct _HuffmanNode {
  int w, p, lc, rc;
} hfn;

typedef struct _HuffmanCode {
  int l;
  unsigned long long v;
} hfc;
/*
 * === Encoding Style: ===
 * l: 6
 * v: 0 1 0 0 0 1 0 0
 *    <---------> * *
 */

hfn tree[256] = {{0}};
int treetop = 128;
hfc code[128] = {{0}};

const char _Input_File[] = "input.txt";
const char _Output_File[] = "output.txt";

int isAvailable(hfn* x) { return x->w > 0 && x->p < 128; }

int scanAndAddToTree() {
  hfn* toadd = tree + treetop;
  int mini = -1, minj = -1;
  int i;
  for (i = 0; i < treetop; i++) {
    if (i == '\n' || !isAvailable(tree + i)) continue;
    if (mini == -1 || (tree + i)->w < (tree + mini)->w) {
      minj = mini;
      mini = i;
    } else if (minj == -1 || (tree + i)->w < (tree + minj)->w) {
      minj = i;
    }
  }
  if (minj == -1) return 0;
  (tree + mini)->p = treetop;
  (tree + minj)->p = treetop;
  toadd->lc = mini;
  toadd->rc = minj;
  toadd->w = (tree + mini)->w + (tree + minj)->w;
  treetop++;
  return 1;
}

hfc travto(char c) {
  int coef = 1;
  int ptr;
  hfc ret = {0};
  ptr = c;
  while (tree[ptr].p != 0) {
    if (tree[tree[ptr].p].rc == ptr) ret.v += coef;
    coef <<= 1;
    ptr = tree[ptr].p;
    (ret.l)++;
  }

  ret.v <<= 8 * sizeof(long long) - ret.l;
  return ret;
}

void dumphft() {
  int i;
  for (i = 0; i < 256; i++) {
    printf("%5d %5d %5d %5d %5d \n", i, tree[i].w, tree[i].p, tree[i].lc,
           tree[i].rc);
  }
}
void dumphfc() {
  int i;
  for (i = 0; i < 128; i++) {
    printf("%5d %016llx %5d\n", i, code[i].v, code[i].l);
  }
}

int main() {
  FILE *input, *output;
  input = fopen(_Input_File, "r");

  {
    // ==== Read In ====
    char c;
    while ((c = fgetc(input)) != EOF) {
      (tree[c].w)++;
    }
    tree['\0'].w = 1;

    // ==== Create Huffman Tree ====
    while (scanAndAddToTree())
      ;  // empty loop!
  }
  fseek(input, 0, 0);
  // dumphft();
  // ==== Create Huffman Code ====
  {
    int i;
    for (i = 0; i < 128; i++) {
      code[i] = travto(i);
    }
    // code[17].v = 0x2200;
  }
  // dumphfc();

  // ==== Output ====
  {
    unsigned long long buf = 0;
    int offset = 0;
    const int endOffset = 8 * sizeof(long long) - 8;
    char c;
    output = fopen(_Output_File, "w");
    while ((c = fgetc(input)) != EOF) {
      if (c == '\n') {
        fputc(c, output);
        continue;
      }
      buf |= (code[c].v >> offset);
      offset += code[c].l;
      // & (-1 << (sizeof(long long) - offset));
      if (offset >= 8)
        while (offset >= 8) {
          unsigned char buf2;
          buf2 = buf >> endOffset;
          buf = buf << 8;
          offset -= 8;
          printf("%hhx", buf2);
          fputc(buf2, output);
        }
      // printf(" %llx %5d\n", buf, offset);
    }
    buf |= (code[0].v >> offset);
    offset += code[0].l;
    while (offset > 0) {
      unsigned char buf2;
      buf2 = buf >> endOffset;
      buf = buf << 8;

      offset -= 8;
      printf("%hhx", buf2);
      fputc(buf2, output);
    }
  }
  fclose(input);
  fclose(output);
  putchar('\n');
  return 0;
}