From a173e49ddc520dbe2e139f93f8217b91e206d277 Mon Sep 17 00:00:00 2001
From: Sam Hocevar <sam@hocevar.net>
Date: Thu, 22 Sep 2011 07:16:02 +0000
Subject: [PATCH] core: implement comparison operators for reals.

---
 src/real.cpp       | 73 +++++++++++++++++++++++++++++++++++++++-------
 src/real.h         |  5 ++++
 test/unit/real.cpp | 21 +++++++++++++
 3 files changed, 89 insertions(+), 10 deletions(-)

diff --git a/src/real.cpp b/src/real.cpp
index f8e45579..548b409a 100644
--- a/src/real.cpp
+++ b/src/real.cpp
@@ -77,17 +77,19 @@ real real::operator +(real const &x) const
     if (x.m_signexp << 1 == 0)
         return *this;
 
-    /* Ensure *this is the larger exponent, and both arguments are
-     * positive (otherwise, switch signs, or replace + with -). */
-    if ((m_signexp << 1) < (x.m_signexp << 1))
-        return x + *this;
-
+    /* Ensure both arguments are positive. Otherwise, switch signs,
+     * or replace + with -). */
     if (m_signexp >> 31)
         return -(-*this + -x);
 
     if (x.m_signexp >> 31)
         return *this - x;
 
+    /* Ensure *this is the larger exponent (no need to be strictly larger,
+     * as in subtraction). Otherwise, switch. */
+    if ((m_signexp << 1) < (x.m_signexp << 1))
+        return x + *this;
+
     real ret;
 
     int e1 = m_signexp - (1 << 30) + 1;
@@ -137,17 +139,18 @@ real real::operator -(real const &x) const
     if (x.m_signexp << 1 == 0)
         return *this;
 
-    /* Ensure *this is the larger exponent, and both arguments are
-     * positive (otherwise, switch signs, or replace - with +). */
-    if ((m_signexp << 1) < (x.m_signexp << 1))
-        return -(x - *this);
-
+    /* Ensure both arguments are positive. Otherwise, switch signs,
+     * or replace - with +). */
     if (m_signexp >> 31)
         return -(-*this + x);
 
     if (x.m_signexp >> 31)
         return (*this) + (-x);
 
+    /* Ensure *this is larger than x */
+    if (*this < x)
+        return -(x - *this);
+
     real ret;
 
     return ret;
@@ -202,6 +205,56 @@ real real::operator *(real const &x) const
     return ret;
 }
 
+bool real::operator <(real const &x) const
+{
+    /* Ensure both numbers are positive */
+    if (m_signexp >> 31)
+        return (x.m_signexp >> 31) ? -*this > -x : true;
+
+    if (x.m_signexp >> 31)
+        return false;
+
+    /* Compare all relevant bits */
+    if (m_signexp != x.m_signexp)
+        return m_signexp < x.m_signexp;
+
+    for (int i = 0; i < BIGITS; i++)
+        if (m_mantissa[i] != x.m_mantissa[i])
+            return m_mantissa[i] < x.m_mantissa[i];
+
+    return false;
+}
+
+bool real::operator <=(real const &x) const
+{
+    return !(*this > x);
+}
+
+bool real::operator >(real const &x) const
+{
+    /* Ensure both numbers are positive */
+    if (m_signexp >> 31)
+        return (x.m_signexp >> 31) ? -*this < -x : false;
+
+    if (x.m_signexp >> 31)
+        return true;
+
+    /* Compare all relevant bits */
+    if (m_signexp != x.m_signexp)
+        return m_signexp > x.m_signexp;
+
+    for (int i = 0; i < BIGITS; i++)
+        if (m_mantissa[i] != x.m_mantissa[i])
+            return m_mantissa[i] > x.m_mantissa[i];
+
+    return false;
+}
+
+bool real::operator >=(real const &x) const
+{
+    return !(*this < x);
+}
+
 void real::print() const
 {
     printf("%x  %08x  ", m_signexp >> 31, (m_signexp << 1) >> 1);
diff --git a/src/real.h b/src/real.h
index 94f27d58..315d0838 100644
--- a/src/real.h
+++ b/src/real.h
@@ -35,6 +35,11 @@ public:
     real operator -(real const &x) const;
     real operator *(real const &x) const;
 
+    bool operator <(real const &x) const;
+    bool operator >(real const &x) const;
+    bool operator <=(real const &x) const;
+    bool operator >=(real const &x) const;
+
     void print() const;
 
 private:
diff --git a/test/unit/real.cpp b/test/unit/real.cpp
index 3fabc757..d84e49c7 100644
--- a/test/unit/real.cpp
+++ b/test/unit/real.cpp
@@ -50,6 +50,27 @@ LOLUNIT_FIXTURE(RealTest)
         LOLUNIT_ASSERT_EQUAL(a4, 0.0f);
     }
 
+    LOLUNIT_TEST(test_real_comp)
+    {
+        LOLUNIT_ASSERT(real(1.0f) > real(0.5f));
+        LOLUNIT_ASSERT(real(1.0f) >= real(0.5f));
+        LOLUNIT_ASSERT(real(1.0f) >= real(1.0f));
+
+        LOLUNIT_ASSERT(real(-1.0f) < real(-0.5f));
+        LOLUNIT_ASSERT(real(-1.0f) <= real(-0.5f));
+        LOLUNIT_ASSERT(real(-1.0f) <= real(-1.0f));
+
+        LOLUNIT_ASSERT(real(-1.0f) < real(0.5f));
+        LOLUNIT_ASSERT(real(-0.5f) < real(1.0f));
+        LOLUNIT_ASSERT(real(-1.0f) <= real(0.5f));
+        LOLUNIT_ASSERT(real(-0.5f) <= real(1.0f));
+
+        LOLUNIT_ASSERT(real(1.0f) > real(-0.5f));
+        LOLUNIT_ASSERT(real(0.5f) > real(-1.0f));
+        LOLUNIT_ASSERT(real(1.0f) >= real(-0.5f));
+        LOLUNIT_ASSERT(real(0.5f) >= real(-1.0f));
+    }
+
     LOLUNIT_TEST(test_real_add)
     {
         float a1 = real(1.0f) + real(0.0f);