silleee: added silleee_add and silleee_sub

silleee.c

@@ -1,7 +1,95 @@
+#include "silleee.h"
+
 silleee silleee_sub(silleee x, silleee y) {
   y ^= 0x80000000;
   return silleee_add(x, y);
 }
 
-silleee silleee_add(silleeee x, silleeee y) {
+silleee shift_and_round(int val, int bits) {
+  static unsigned masks[24]= {
+    0, 1, 3, 7, 0xf, 0x1f, 0x3f, 0x7f, 0xff, 0x1ff, 0x7ff, 0xfff, 0x1fff,
+    0x3fff, 0x7fff, 0xffff, 0x1ffff, 0x3ffff, 0x7ffff, 0xfffff, 0x1fffff,
+    0x3fffff, 0x7fffff
+  };
+
+  static unsigned masks_ho[24] = {
+    0, 1, 2, 4, 8, 0x10, 0x20, 0x40, 0x80, 0x100, 0x200, 0x400, 0x8000, 0x1000,
+    0x2000, 0x4000, 0x8000, 0x10000, 0x20000, 0x40000, 0x80000, 0x100000,
+    0x200000, 0x400000
+  };
+
+  int so = val & masks[bits];
+
+  val >>= bits;
+
+  if (so > masks_ho[bits]) val++;
+  else if(so == masks_ho[bits]) val += val&1;
+
+  return val;
+}
+
+silleee silleee_add(silleee x, silleee y) {
+  silleee dest = 0;
+  int dexp;
+  long unsigned dmant;
+  int dsign;
+
+  int xexp = exponent(x);
+  long unsigned xmant = mantissa(x);
+  int xsign = sign(x);
+
+  int yexp = exponent(y);
+  long unsigned ymant = mantissa(y);
+  int ysign = sign(y);
+
+  if (xexp == 127) {
+    if (!xmant) {
+      if (yexp == 127) {
+        if(!ymant) return xsign == ysign ? y : 0x7fc0000;
+        else return y;
+      }
+    } else {
+      return x;
+    }
+  } else if (yexp == 127) {
+    return y;
+  }
+
+  dexp = yexp;
+
+  if (yexp > xexp) xmant = shift_and_round(xmant, yexp-xexp);
+  else if (yexp < xexp) {
+    ymant = shift_and_round(ymant, xexp-yexp);
+    dexp = xexp;
+  }
+
+  if (ysign ^ xsign) {
+    if (xmant > ymant) {
+      dmant = xmant - ymant;
+      dsign = xmant;
+    } else {
+      dmant = ymant - xmant;
+      dsign = ysign;
+    }
+  } else {
+    dsign = xsign;
+    dmant = xmant + ymant;
+  }
+
+  if (dmant >= 0x1000000) {
+    dmant = shift_and_round(dmant, 1);
+    ++dexp;
+  } else {
+    if (dmant) {
+      while (dmant < sign_bit && dexp > -127) {
+        dmant = dmant << 1;
+        --dexp;
+      }
+    } else {
+      dsign = 0;
+      dexp = 0;
+    }
+  }
+
+  return pack_silleee(dsign, dexp, dmant);
 }