do not un/reSign constants

1 files changed, 30 insertions, 0 deletions

diff --git a/src/library.js b/src/library.js
index b875e131..08daceb1 100644
--- a/src/library.js
+++ b/src/library.js
@@ -1230,3 +1230,33 @@ var Library = {
   }
 };
 
+
+// 'Runtime' functions that need preprocessor parsing like library functions
+
+// Converts a value we have as signed, into an unsigned value. For
+// example, -1 in int32 would be a very large number as unsigned.
+function unSign(value, bits, ignore) {
+  if (value >= 0) return value;
+#if CHECK_SIGNS
+  if (!ignore) CorrectionsMonitor.note('UnSign');
+#endif
+  return bits <= 32 ? 2*Math.abs(1 << (bits-1)) + value // Need some trickery, since if bits == 32, we are right at the limit of the bits JS uses in bitshifts
+                    : Math.pow(2, bits)         + value;
+  // TODO: clean up previous line
+}
+
+// Converts a value we have as unsigned, into a signed value. For
+// example, 200 in a uint8 would be a negative number.
+function reSign(value, bits, ignore) {
+  if (value <= 0) return value;
+  var half = bits <= 32 ? Math.abs(1 << (bits-1)) // abs is needed if bits == 32
+                        : Math.pow(2, bits-1);
+  if (value >= half) {
+#if CHECK_SIGNS
+  if (!ignore) CorrectionsMonitor.note('ReSign');
+#endif
+    value = -2*half + value; // Cannot bitshift half, as it may be at the limit of the bits JS uses in bitshifts
+  }
+  return value;
+}
+