Changeset 1017 for trunk/src/real.cppTweet

Timestamp:

Oct 12, 2011, 12:01:44 AM (12 years ago)

Author:

sam

Message:

core: fix an accuracy error in real::re() and real::sqrt() introduced in
the 16-to-32-bit refactoring.

File:

• trunk/src/real.cpp (modified) (4 diffs)

trunk/src/real.cpp

@@ -23 +23 @@
 {
 
-static int const BIGIT_BITS = 32;
-
 real::real(float f) { *this = (double)f; }
 real::real(int i) { *this = (double)i; }
@@ -501 +499 @@
     ret.m_signexp |= (exponent - 1) & 0x7fffffffu;
 
-    /* FIXME: log2(BIGITS) steps of Newton-Raphson seems to be enough for
+    /* FIXME: 1+log2(BIGITS) steps of Newton-Raphson seems to be enough for
      * convergence, but this hasn't been checked seriously. */
-    for (int i = 2; i < real::BIGITS; i *= 2)
+    for (int i = 1; i <= real::BIGITS; i *= 2)
         ret = ret * (real::R_2 - ret * x);
 
@@ -545 +543 @@
     ret.m_signexp |= exponent & 0x7fffffffu;
 
-    /* FIXME: log2(BIGITS) steps of Newton-Raphson seems to be enough for
+    /* FIXME: 1+log2(BIGITS) steps of Newton-Raphson seems to be enough for
      * convergence, but this hasn't been checked seriously. */
-    for (int i = 2; i < real::BIGITS; i *= 2)
+    for (int i = 1; i <= real::BIGITS; i *= 2)
     {
         ret = ret * (real::R_3 - ret * ret * x);
@@ -669 +667 @@
         if (exponent <= 0)
             ret.m_mantissa[i] = 0;
-        else if (exponent < BIGIT_BITS)
-            ret.m_mantissa[i] &= ~((1 << (BIGIT_BITS - exponent)) - 1);
-
-        exponent -= BIGIT_BITS;
+        else if (exponent < real::BIGIT_BITS)
+            ret.m_mantissa[i] &= ~((1 << (real::BIGIT_BITS - exponent)) - 1);
+
+        exponent -= real::BIGIT_BITS;
     }