added demand paging algorithms

demand-paging/main.typ

@@ -0,0 +1,24 @@
+#import "utils.typ": sim-demand-paging
+
+#set document(title: "Demand paging algorithms")
+#set page(width: auto, height: auto, margin: 1cm)
+#set text(font: "Source Sans 3")
+
+#let requests = (7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 1, 2, 0, 1, 7, 0 , 1)
+
+#align(center, text(size: 1.2em)[*Demand paging algorithms*])
+
+#figure(
+  sim-demand-paging(requests, "FIFO"),
+  caption: [Demand Paging: FIFO]
+)
+
+#figure(
+  sim-demand-paging(requests, "OPT"),
+  caption: [Demand Paging: OPT]
+)
+
+#figure(
+  sim-demand-paging(requests, "LRU"),
+  caption: [Demand Paging: LRU]
+)

demand-paging/utils.typ

@@ -0,0 +1,84 @@
+#let sim-demand-paging(size: 3, requests, algo) = {
+  let mem = ()
+
+  let j = 0
+  let last-used = (:)
+  
+  let states = ()
+  let cells = ()
+  let faults = 0
+  
+  for (i, req) in requests.enumerate() {
+    // In memory
+    if req in mem {
+      cells.push(req)
+    
+    // Not in memory but enough space
+    } else if mem.len() < size {
+      mem.push(req)
+      cells.push(req)
+    
+    // Page fault
+    } else {
+      faults += 1
+
+      if algo == "FIFO" {
+        mem.at(j) = req
+        j = calc.rem(j + 1, size)
+      
+      } else if algo == "OPT" {
+        let future = requests.slice(i + 1)
+        let dists = mem.map(v => {
+          let pos = future.position(v2 => v2 == v)
+          return if pos == none {calc.inf} else {pos}
+        })
+        let max = calc.max(..dists)
+        let k = dists.position(v => v == max)
+        mem.at(k) = req
+      
+      } else if algo == "LRU" {
+        let k = mem.enumerate()
+                   .map(p => (
+                     p.first(),
+                     last-used.at(
+                       str(p.last())
+                     )
+                   ))
+                   .sorted(key: p => p.last())
+                   .first()
+                   .first()
+
+        mem.at(k) = req
+      }
+      
+      cells.push(grid.cell(fill: red.lighten(40%), str(req)))
+    }
+    last-used.insert(str(req), i)
+
+    states.push(mem)
+  }
+
+  cells.insert(0, grid.cell(
+    rowspan: size + 1,
+    stroke: black,
+    inset: (x: 0.4em, y: 0.4em),
+    rotate(-90deg, reflow: true)[Faults: #faults]
+  ))
+
+  for i in range(size) {
+    cells += states.map(s => s.at(i, default: none))
+  }
+
+  grid(
+    columns: requests.len() + 1,
+    inset: (x: 0.2em, y: 0.4em),
+    stroke: (x, y) => if y != 0 {
+      black + .5pt
+    },
+    column-gutter: 0.6em,
+    row-gutter: (0.4em,) + (0pt,) * size,
+    align: center + horizon,
+    fill: (x, y) => if y != 0 {blue.lighten(60%)},
+    ..cells.map(c => if type(c) == int {str(c)} else {c})
+  )
+}