Changeset 94b696c in mainline

Timestamp:

2012-11-24T22:38:36Z (11 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

02ce8a0

Parents:

d4cd7e5

Message:

Fix detection of rounding overflow for 64-bit floats.

File:

• uspace/lib/softfloat/common.c (modified) (1 diff)

uspace/lib/softfloat/common.c

@@ -307 +307 @@
 /**
  * Round and normalize number expressed by exponent and fraction with
- * first bit (equal to hidden bit) at 62nd bit.
+ * first bit (equal to hidden bit) at bit 62.
  *
  * @param exp Exponent part.
- * @param fraction Fraction with hidden bit shifted to 62nd bit.
+ * @param fraction Fraction with hidden bit shifted to bit 62.
  */
 void round_float64(int32_t *exp, uint64_t *fraction)
 {
-        /* rounding - if first bit after fraction is set then round up */
+        /*
+         * Rounding - if first bit after fraction is set then round up.
+         */
+
+        /*
+         * Add 1 to the least significant bit of the fraction respecting the
+         * current shift to bit 62 and see if there will be a carry to bit 63.
+         */
         (*fraction) += (0x1 << (64 - FLOAT64_FRACTION_SIZE - 3));
         
+        /* See if there was a carry to bit 63. */
         if ((*fraction) & 
-            (FLOAT64_HIDDEN_BIT_MASK << (64 - FLOAT64_FRACTION_SIZE - 3))) {
+            (FLOAT64_HIDDEN_BIT_MASK << (64 - FLOAT64_FRACTION_SIZE - 1))) {
                 /* rounding overflow */
                 ++(*exp);