Initial data commit

Task/Bitwise-IO/C/bitwise-io.c

@@ -0,0 +1,114 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+typedef uint8_t byte;
+typedef struct {
+    FILE *fp;
+    uint32_t accu;
+    int bits;
+} bit_io_t, *bit_filter;
+
+bit_filter b_attach(FILE *f)
+{
+    bit_filter b = malloc(sizeof(bit_io_t));
+    b->bits = b->accu = 0;
+    b->fp = f;
+    return b;
+}
+
+void b_write(byte *buf, size_t n_bits, size_t shift, bit_filter bf)
+{
+    uint32_t accu = bf->accu;
+    int bits = bf->bits;
+
+    buf += shift / 8;
+    shift %= 8;
+
+    while (n_bits || bits >= 8) {
+        while (bits >= 8) {
+            bits -= 8;
+            fputc(accu >> bits, bf->fp);
+            accu &= (1 << bits) - 1;
+        }
+        while (bits < 8 && n_bits) {
+            accu = (accu << 1) | (((128 >> shift) & *buf) >> (7 - shift));
+            --n_bits;
+            bits++;
+            if (++shift == 8) {
+                shift = 0;
+                buf++;
+            }
+        }
+    }
+    bf->accu = accu;
+    bf->bits = bits;
+}
+
+size_t b_read(byte *buf, size_t n_bits, size_t shift, bit_filter bf)
+{
+    uint32_t accu = bf->accu;
+    int bits = bf->bits;
+    int mask, i = 0;
+
+    buf += shift / 8;
+    shift %= 8;
+
+    while (n_bits) {
+        while (bits && n_bits) {
+            mask = 128 >> shift;
+            if (accu & (1 << (bits - 1))) *buf |= mask;
+            else *buf &= ~mask;
+
+            n_bits--;
+            bits--;
+
+            if (++shift >= 8) {
+                shift = 0;
+                buf++;
+            }
+        }
+        if (!n_bits) break;
+        accu = (accu << 8) | fgetc(bf->fp);
+        bits += 8;
+    }
+    bf->accu = accu;
+    bf->bits = bits;
+
+    return i;
+}
+
+void b_detach(bit_filter bf)
+{
+    if (bf->bits) {
+        bf->accu <<= 8 - bf->bits;
+        fputc(bf->accu, bf->fp);
+    }
+    free(bf);
+}
+
+int main()
+{
+    unsigned char s[] = "abcdefghijk";
+    unsigned char s2[11] = {0};
+    int i;
+
+    FILE *f = fopen("test.bin", "wb");
+    bit_filter b = b_attach(f);
+    /* for each byte in s, write 7 bits skipping 1 */
+    for (i = 0; i < 10; i++) b_write(s + i, 7, 1, b);
+    b_detach(b);
+    fclose(f);
+
+    /* read 7 bits and expand to each byte of s2 skipping 1 bit */
+    f = fopen("test.bin", "rb");
+    b = b_attach(f);
+    for (i = 0; i < 10; i++) b_read(s2 + i, 7, 1, b);
+    b_detach(b);
+    fclose(f);
+
+    printf("%10s\n", s2); /* should be the same first 10 bytes as in s */
+
+    return 0;
+}