a1k0n · September 2, 2020 20:23 · Sep 2, 2020
diff --git a/donut_integer.c b/donut_integer.c
@@ -0,0 +1,58 @@
+// the donut code with fixed-point arithmetic; no sines, cosines, square roots, or anything.
+// a1k0n 2020
+
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#define R(mul,shift,x,y) \
+  _=x; \
+  x -= mul*y>>shift; \
+  y += mul*_>>shift; \
+  _ = 3145728-x*x-y*y>>11; \
+  x = x*_>>10; \
+  y = y*_>>10;
+
+char b[1760], z[1760];
+
+void main() {
+  int sA=1024,cA=0,sB=1024,cB=0,_;
+  for (;;) {
+    memset(b, 32, 1760);  // text buffer
+    memset(z, 127, 1760);   // z buffer
+    int sj=0, cj=1024;
+    for (int j = 0; j < 90; j++) {
+      int si = 0, ci = 1024;  // sine and cosine of angle i
+      for (int i = 0; i < 324; i++) {
+        int R1 = 1, R2 = 2048, K2 = 5120*1024;
+
+        int x0 = R1*cj + R2,
+            x1 = ci*x0 >> 10,
+            x2 = cA*sj >> 10,
+            x3 = si*x0 >> 10,
+            x4 = R1*x2 - (sA*x3 >> 10),
+            x5 = sA*sj >> 10,
+            x6 = K2 + R1*1024*x5 + cA*x3,
+            x7 = cj*si >> 10,
+            x = 40 + 30*(cB*x1 - sB*x4)/x6,
+            y = 12 + 15*(cB*x4 + sB*x1)/x6,
+            N = (-cA*x7 - cB*((-sA*x7>>10) + x2) - ci*(cj*sB >> 10) >> 10) - x5 >> 7;
+
+        int o = x + 80 * y;
+        char zz = (x6-K2)>>15;
+        if (22 > y && y > 0 && x > 0 && 80 > x && zz < z[o]) {
+          z[o] = zz;
+          b[o] = ".,-~:;=!*#$@"[N > 0 ? N : 0];
+        }
+        R(5, 8, ci, si)  // rotate i
+      }
+      R(9, 7, cj, sj)  // rotate j
+    }
+    for (int k = 0; 1761 > k; k++)
+      putchar(k % 80 ? b[k] : 10);
+    R(5, 7, cA, sA);
+    R(5, 8, cB, sB);
+    usleep(15000);
+    printf("\x1b[23A");
+  }
+}