core: fix real unary minus and handle negative numbers in additions.

src/real.cpp

@@ -53,7 +53,7 @@ real::operator float() const
     uint32_t exponent = m_signexp & 0x7fffffffu;
     uint32_t mantissa = (m_mantissa[0] << 7) | (m_mantissa[1] >> 9);
 
-    int e = (int)(m_signexp & 0x7fffffffu) - (1 << 30) + (1 << 7);
+    int e = (int)exponent - (1 << 30) + (1 << 7);
 
     if (e < 0)
         u.x = sign;
@@ -65,25 +65,33 @@ real::operator float() const
     return u.f;
 }
 
-real real::operator -()
+real real::operator -() const
 {
-    m_signexp ^= 0x80000000u;
-    return *this;
+    real ret = *this;
+    ret.m_signexp ^= 0x80000000u;
+    return ret;
 }
 
 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;
 
-    if (x.m_signexp << 1 == 0)
-        return *this;
+    if (m_signexp >> 31)
+        return -(-*this + -x);
+
+    if (x.m_signexp >> 31)
+        return *this - x;
 
-    /* For now, assume both numbers are positive. */
     real ret;
 
-    int e1 = (m_signexp & 0x7fffffffu) - (1 << 30) + 1;
-    int e2 = (x.m_signexp & 0x7fffffffu) - (1 << 30) + 1;
+    int e1 = m_signexp - (1 << 30) + 1;
+    int e2 = x.m_signexp - (1 << 30) + 1;
 
     int bigoff = (e1 - e2) / (sizeof(uint16_t) * 8);
     int off = e1 - e2 - bigoff * (sizeof(uint16_t) * 8);
@@ -91,20 +99,20 @@ real real::operator +(real const &x) const
     ret.m_signexp = m_signexp;
 
     uint32_t carry = 0;
-    for (int i = 0; i < BIGITS; i++)
+    for (int i = BIGITS; i--; )
     {
-        carry = m_mantissa[BIGITS - 1 - i];
-        if (BIGITS - 1 - i - bigoff >= 0)
-            carry += x.m_mantissa[BIGITS - 1 - i - bigoff] >> off;
-        else if (BIGITS - 1 - i - bigoff == -1)
+        carry = m_mantissa[i];
+        if (i - bigoff >= 0)
+            carry += x.m_mantissa[i - bigoff] >> off;
+        else if (i - bigoff == -1)
             carry += 0x0001u >> off;
 
-        if (BIGITS - 1 - i - bigoff - 1 >= 0)
-            carry += (x.m_mantissa[BIGITS - 1 - i - bigoff - 1] << (16 - off)) & 0xffffu;
-        else if (BIGITS - 1 - i - bigoff - 1 == -1)
+        if (i - bigoff > 0)
+            carry += (x.m_mantissa[i - bigoff - 1] << (16 - off)) & 0xffffu;
+        else if (i - bigoff == 0)
             carry += 0x0001u << (16 - off);
 
-        ret.m_mantissa[BIGITS - 1 - i] = carry;
+        ret.m_mantissa[i] = carry;
         carry >>= 16;
     }
 
@@ -124,6 +132,27 @@ real real::operator +(real const &x) const
     return ret;
 }
 
+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);
+
+    if (m_signexp >> 31)
+        return -(-*this + x);
+
+    if (x.m_signexp >> 31)
+        return (*this) + (-x);
+
+    real ret;
+
+    return ret;
+}
+
 real real::operator *(real const &x) const
 {
     real ret;

src/real.h

@@ -30,8 +30,9 @@ public:
     real(float f);
 
     operator float() const;
-    real operator -();
+    real operator -() const;
     real operator +(real const &x) const;
+    real operator -(real const &x) const;
     real operator *(real const &x) const;
 
     void print() const;

test/unit/real.cpp

@@ -22,7 +22,6 @@ namespace lol
 
 LOLUNIT_FIXTURE(RealTest)
 {
-public:
     LOLUNIT_TEST(test_real_from_float)
     {
         float a1 = real(0.0f);
@@ -53,6 +52,30 @@ public:
 
     LOLUNIT_TEST(test_real_add)
     {
+        float a1 = real(1.0f) + real(0.0f);
+        float a2 = real(0.0f) + real(1.0f);
+        float a3 = real(1.0f) + real(1.0f);
+        float a4 = real(-1.0f) + real(-1.0f);
+        float a5 = real(1.0f) + real(0.125f);
+
+        LOLUNIT_ASSERT_EQUAL(a1, 1.0f);
+        LOLUNIT_ASSERT_EQUAL(a2, 1.0f);
+        LOLUNIT_ASSERT_EQUAL(a3, 2.0f);
+        LOLUNIT_ASSERT_EQUAL(a4, -2.0f);
+        LOLUNIT_ASSERT_EQUAL(a5, 1.125f);
+    }
+
+    LOLUNIT_TEST(test_real_sub)
+    {
+#if 0
+printf("\n");
+real k(1.25f);
+k.print();
+real l(1.0f);
+l.print();
+real m = k - l;
+m.print();
+#endif
         LOLUNIT_ASSERT(true);
     }