Use <bit> instead of platform-specific intrinsics

Change-Id: I79636ff9c3b2fe601b0b3c94a111b36af0011775
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/164131
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

1 files changed, 6 insertions, 23 deletions

diff --git a/sal/rtl/math.cxx b/sal/rtl/math.cxx
index fe45b90a8297..5b6c780b5001 100644
--- a/sal/rtl/math.cxx
+++ b/sal/rtl/math.cxx
@@ -24,6 +24,7 @@
 #include <rtl/math.hxx>
 
 #include <algorithm>
+#include <bit>
 #include <cassert>
 #include <cfenv>
 #include <cmath>
@@ -118,18 +119,6 @@ bool isRepresentableInteger(double fAbsValue)
     return nInt == fAbsValue;
 }
 
-// Returns 1-based index of least significant bit in a number, or zero if number is zero
-int findFirstSetBit(unsigned n)
-{
-#if defined _WIN32
-    unsigned long pos;
-    unsigned char bNonZero = _BitScanForward(&pos, n);
-    return (bNonZero == 0) ? 0 : pos + 1;
-#else
-    return __builtin_ffs(n);
-#endif
-}
-
 /** Returns number of binary bits for fractional part of the number
     Expects a proper non-negative double value, not +-INF, not NAN
  */
@@ -138,19 +127,13 @@ int getBitsInFracPart(double fAbsValue)
     assert(std::isfinite(fAbsValue) && fAbsValue >= 0.0);
     if (fAbsValue == 0.0)
         return 0;
-    auto pValParts = reinterpret_cast<const sal_math_Double*>(&fAbsValue);
-    int nExponent = pValParts->inf_parts.exponent - 1023;
+    auto& rValParts = reinterpret_cast<const sal_math_Double*>(&fAbsValue)->parts;
+    int nExponent = rValParts.exponent - 1023;
     if (nExponent >= 52)
         return 0; // All bits in fraction are in integer part of the number
-    int nLeastSignificant = findFirstSetBit(pValParts->inf_parts.fraction_lo);
-    if (nLeastSignificant == 0)
-    {
-        nLeastSignificant = findFirstSetBit(pValParts->inf_parts.fraction_hi);
-        if (nLeastSignificant == 0)
-            nLeastSignificant = 53; // the implied leading 1 is the least significant
-        else
-            nLeastSignificant += 32;
-    }
+    int nLeastSignificant = rValParts.fraction
+                                ? std::countr_zero(rValParts.fraction) + 1
+                                : 53; // the implied leading 1 is the least significant
     int nFracSignificant = 53 - nLeastSignificant;
     int nBitsInFracPart = nFracSignificant - nExponent;