116 lines
3.5 KiB
C
116 lines
3.5 KiB
C
#include "bitmap.h"
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#include <stdio.h>
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// IMPLEMENTED FOR YOU
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// Utility function to print out an array of char as bits
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// Print the entire bitmap. Arguments: The bitmap itself, and the length of the
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// bitmap Each bit of the bitmap represents 1 byte of memory. 0 = free, 1 =
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// allocated. map: The bitmap itself, an array of unsigned char.
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// Each bit of the bitmap represents one byte of memory
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// len: The length of the bitmap array in characters
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//
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// Returns: Nothing
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void print_map(unsigned char *map, int len) {
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int i, j;
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for (i = 0; i < len; i++) {
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unsigned char mask = 0b10000000;
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for (j = 0; j < 8; j++) {
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if (map[i] & mask)
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printf("1");
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else
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printf("0");
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mask = mask >> 1;
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}
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printf(" ");
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}
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printf("\n");
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}
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// Search the bitmap for the required number of zeroes (representing
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// free bytes of memory). Returns index of first stretch of 0s
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// that meet the criteria. You can use this as an index into
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// an array of char that represents the process heap
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// bitmap = Bitmap declared as an array of unsigned char
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// len = Length of bitmap in characters
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// num_zeroes = Length of string of 0's required
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// Returns: Index to stretch of 0's of required length, -1 if no such stretch
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// can be found
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long search_map(unsigned char *bitmap, int len, long num_zeroes) {
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int count = 0;
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for (int i = 0; i < len; i++) {
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unsigned char mask = 0b10000000;
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for (int j = 0; j < 8; j++) {
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if ((bitmap[i] & mask) == 0) {
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count++;
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if (count == num_zeroes) {
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return i * 8 + j - num_zeroes + 1;
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}
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} else {
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count = 0;
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}
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mask >>= 1;
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}
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}
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return -1;
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} // main
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// Set map bits to 0 or 1 depending on whether value is non-zero
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// map = Bitmap, declared as an array of unsigned char
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// start = Starting index to mark as 1 or 0
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// length = Number of bits to mark
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// value = Value to mark the bits as. value = 0 marks the bits
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// as 0, non-zero marks the bits as 1
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// Returns: Nothing
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// start: 7
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// length: 4
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// value: 1
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void set_map(unsigned char *map, long start, long length, int value) {
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// printf("set_map with start=%ld, length=%ld val=%d\n", start, length,
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// value);
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int starting_index = start / 8;
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for (int i = 0; i < length; i++) {
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int currIdx = (start + i) / 8;
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int currOffset = (start + i) % 8;
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int mask = 0b10000000;
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if (value == 0) {
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map[currIdx] &= ~(mask >> currOffset);
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} else {
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map[currIdx] |= (mask >> currOffset);
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}
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}
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// the ~(1<< offset) is a nice trick to create, for example
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// ~(1 << 2) = 1111 1011
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// By anding this, you can set the value to 0 for that bit
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// map[char_index + length_index] &= ~(1 << length_offset);
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// the (1<< offset) is a nice trick to create, for example
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// (1 << 2) = 0000 0100
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// likewise, set the given bit to 1
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// map[char_index + length_index] |= (1 << length_offset);
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}
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// IMPLEMENTED FOR YOU
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// Marks a stretch of bits as "1", representing allocated memory
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// map = Bitmap declared as array of unsigned char
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// start = Starting index to mark
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// length = Number of bits to mark as "1"
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void allocate_map(unsigned char *map, long start, long length) {
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set_map(map, start, length, 1);
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}
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// IMPLEMENTED FOR YOU
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// Marks a stretch of bits as "0", representing allocated memory
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// map = Bitmap declared as array of unsigned char
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// start = Starting index to mark
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// length = Number of bits to mark as "0"
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void free_map(unsigned char *map, long start, long length) {
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set_map(map, start, length, 0);
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}
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