78 lines
2.6 KiB
C
78 lines
2.6 KiB
C
#include <stdio.h>
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#include <stdlib.h> // For malloc, free
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// C program for LRU Page Replacement Simulation
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// Optimized for minimal code size (e.g., for writing on paper)
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int main() {
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int nf, np, i, j, pg, idx, lru, pf = 0, time = 0, min_t;
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// nf=num frames, np=num pages, pf=page faults, time=logical clock
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// idx=found index, lru=least recently used index, pg=current page
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// Input frame count (nf) and page reference string length (np)
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printf("Frames Pages:"); scanf("%d%d", &nf, &np);
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// Dynamic Allocation
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int *f = malloc(nf * sizeof(int)); // f: frames array
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int *c = malloc(nf * sizeof(int)); // c: counter/lru time array
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int *p = malloc(np * sizeof(int)); // p: page reference string array
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// Input page reference string
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printf("Pages:");
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for(i=0; i<np; ) scanf("%d", p+i++); // Read pages into p
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// Initialize frames to -1 (empty)
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for(i=0; i<nf; i++) f[i]=-1; // Can also use for(i=nf;i--;)f[i]=-1;
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// --- LRU Algorithm ---
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for(i=0; i<np; i++) { // Iterate through page reference string
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pg = p[i]; // Current page
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idx = -1; // Reset found index
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// 1. Search if page 'pg' is already in frames 'f'
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for(j=0; j<nf; j++) {
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if(f[j] == pg) {
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idx = j; // Page found at index j
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break;
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}
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}
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if(idx != -1) { // 2a. Page Hit
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c[idx] = ++time; // Update last used time for the hit page
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} else { // 2b. Page Fault
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pf++; // Increment page fault counter
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lru = 0; // Index to replace (default to 0)
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min_t = 0x7FFFFFFF; // Initialize minimum time to max int
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// 3. Find replacement slot: first empty (-1) or LRU
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for(j=0; j<nf; j++) {
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if(f[j] == -1) { // Found an empty frame
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lru = j;
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break; // Use the first empty frame
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}
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if(c[j] < min_t) { // Track frame with the smallest time (LRU)
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min_t = c[j];
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lru = j;
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}
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}
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// 'lru' now holds index of empty slot or the least recently used page
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// 4. Replace frame and update its time
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f[lru] = pg;
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c[lru] = ++time;
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}
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// Optional: print frame state after each step (for debugging)
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// printf(" (%d):",pg); for(j=0; j<nf; j++)printf(" %d", f[j]==-1?-1:f[j]); puts("");
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}
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// --- End Algorithm ---
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// Output total page faults
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printf("Faults: %d\n", pf);
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// Free dynamically allocated memory
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free(f);
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free(c);
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free(p);
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return 0; // End of program
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}
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