Fix issue 20205 - std.math: Wrong result for abs(int.min)

Author: Berni

std/math.d

@@ -131,7 +131,7 @@ static import core.math;
 static import core.stdc.math;
 static import core.stdc.fenv;
 import std.traits :  CommonType, isFloatingPoint, isIntegral, isNumeric,
-    isSigned, isUnsigned, Largest, Unqual;
+    isSigned, isUnsigned, Largest, Unqual, Unsigned;
 
 version (LDC)
 {
@@ -590,21 +590,23 @@ template isDeprecatedComplex(T)
  *     the return type will be the same as the input;
  */
 auto abs(Num)(Num x)
+// first line is needed until transition due to issue 16997 ended
 if ((is(Unqual!Num == short) || is(Unqual!Num == byte)) ||
     (is(typeof(Num.init >= 0)) && is(typeof(-Num.init))))
 {
-    static if (isFloatingPoint!(Num))
+    static if (isFloatingPoint!Num)
         return fabs(x);
-    else
+    else static if (isIntegral!Num)
     {
-        static if (is(Unqual!Num == short) || is(Unqual!Num == byte))
-            return x >= 0 ? x : cast(Num) -int(x);
-        else
-            return x >= 0 ? x : -x;
+        // (0 - x) is a workaround until transition due to issue 16997 ended
+        static if (isSigned!Num) if (x < 0) return cast(Unsigned!Num)(0 - x);
+        return x;
     }
+    else
+        return x >= 0 ? x : -x;
 }
 
-/// ditto
+///
 @safe pure nothrow @nogc unittest
 {
     assert(isIdentical(abs(-0.0L), 0.0L));
@@ -614,6 +616,18 @@ if ((is(Unqual!Num == short) || is(Unqual!Num == byte)) ||
     assert(abs(2321312L)  == 2321312L);
 }
 
+@safe pure nothrow @nogc unittest
+{
+    assert(abs(byte.min)==128U);
+    assert(abs(short.min)==32768U);
+    assert(abs(int.min)==2147483648U);
+    assert(abs(long.min)==9223372036854775808UL);
+    assert(abs(byte.max)==127U);
+    assert(abs(short.max)==32767U);
+    assert(abs(int.max)==2147483647U);
+    assert(abs(long.max)==9223372036854775807UL);
+}
+
 version (TestComplex)
 deprecated
 @safe pure nothrow @nogc unittest