Added negative zero preprocessor constants

We had some discussions already when we started using negative
zero that it could be fragile on some compilers, and apparently
PGI is one of them. Maybe not the most important target, but it
makes sense to have a common constant in one place, and it can
also save some cycles in tight loops to clearly separate float
from double versions so we avoid extra precision conversions.

Change-Id: Id30a536b4f99f0310bfb2ec5185275c466cf5e07

diff --git a/src/gromacs/legacyheaders/types/simple.h b/src/gromacs/legacyheaders/types/simple.h
index bf1a5216af6ce355a904433518145c5e11c3f27d..de1ebdcb77865105721847e8926eb4158ac4eef7 100644 (file)
--- a/src/gromacs/legacyheaders/types/simple.h
+++ b/src/gromacs/legacyheaders/types/simple.h
@@ -109,6 +109,25 @@ typedef int         atom_id;      /* To indicate an atoms id         */
 /*! \brief Minimum single precision value */
 #define GMX_FLOAT_MIN    1.175494351E-38F
 
+#ifdef __PGI
+/* The portland group x86 C/C++ compilers do not treat negative zero initializers
+ * correctly, but "optimizes" them to positive zero, so we implement it explicitly.
+ * These constructs are optimized to simple loads at compile time. If you want to
+ * use them on other compilers those have to support gcc preprocessor extensions.
+ * Note: These initializers might be sensitive to the endianness (which can
+ * be different for byte and word order), so check that it works for your platform
+ * and add a separate section if necessary before adding to the ifdef above.
+ */
+#    define GMX_DOUBLE_NEGZERO  ({ const union { int  di[2]; double d; } _gmx_dzero = {0, -2147483648}; _gmx_dzero.d; })
+#    define GMX_FLOAT_NEGZERO   ({ const union { int  fi; float f; } _gmx_fzero = {-2147483648}; _gmx_fzero.f; })
+#else
+/*! \brief Negative zero in double */
+#    define GMX_DOUBLE_NEGZERO  (-0.0)
+
+/*! \brief Negative zero in float */
+#    define GMX_FLOAT_NEGZERO   (-0.0f)
+#endif
+
 
 /* Check whether we already have a real type! */
 #ifdef GMX_DOUBLE
@@ -118,10 +137,11 @@ typedef double      real;
 #define HAVE_REAL
 #endif
 
-#define GMX_MPI_REAL    MPI_DOUBLE
-#define GMX_REAL_EPS    GMX_DOUBLE_EPS
-#define GMX_REAL_MIN    GMX_DOUBLE_MIN
-#define GMX_REAL_MAX    GMX_DOUBLE_MAX
+#define GMX_MPI_REAL      MPI_DOUBLE
+#define GMX_REAL_EPS      GMX_DOUBLE_EPS
+#define GMX_REAL_MIN      GMX_DOUBLE_MIN
+#define GMX_REAL_MAX      GMX_DOUBLE_MAX
+#define GMX_REAL_NEGZERO  GMX_DOUBLE_NEGZERO
 #define gmx_real_fullprecision_pfmt "%21.14e"
 #else
 
@@ -130,10 +150,11 @@ typedef float           real;
 #define HAVE_REAL
 #endif
 
-#define GMX_MPI_REAL    MPI_FLOAT
-#define GMX_REAL_EPS    GMX_FLOAT_EPS
-#define GMX_REAL_MIN    GMX_FLOAT_MIN
-#define GMX_REAL_MAX    GMX_FLOAT_MAX
+#define GMX_MPI_REAL      MPI_FLOAT
+#define GMX_REAL_EPS      GMX_FLOAT_EPS
+#define GMX_REAL_MIN      GMX_FLOAT_MIN
+#define GMX_REAL_MAX      GMX_FLOAT_MAX
+#define GMX_REAL_NEGZERO  GMX_FLOAT_NEGZERO
 #define gmx_real_fullprecision_pfmt "%14.7e"
 #endif
 

diff --git a/src/gromacs/simd/impl_intel_mic/impl_intel_mic.h b/src/gromacs/simd/impl_intel_mic/impl_intel_mic.h
index 8c62c3a43b8e070a9d81f68376ce218a1ee52f44..e3d49126f0ebf5132ad8744c2e2caa198f591f18 100644 (file)
--- a/src/gromacs/simd/impl_intel_mic/impl_intel_mic.h
+++ b/src/gromacs/simd/impl_intel_mic/impl_intel_mic.h
@@ -98,7 +98,7 @@
 #define gmx_simd_xor_f(a, b)        _mm512_castsi512_ps(_mm512_xor_epi32(_mm512_castps_si512(a), _mm512_castps_si512(b)))
 #define gmx_simd_rsqrt_f           _mm512_rsqrt23_ps
 #define gmx_simd_rcp_f             _mm512_rcp23_ps
-#define gmx_simd_fabs_f(x)         gmx_simd_andnot_f(_mm512_set1_ps(-0.0), x)
+#define gmx_simd_fabs_f(x)         gmx_simd_andnot_f(_mm512_set1_ps(GMX_FLOAT_NEGZERO), x)
 #define gmx_simd_fneg_f(x)         _mm512_addn_ps(x, _mm512_setzero_ps())
 #define gmx_simd_max_f             _mm512_gmax_ps
 #define gmx_simd_min_f             _mm512_gmin_ps
@@ -189,7 +189,7 @@
 #define gmx_simd_xor_d(a, b)       _mm512_castsi512_pd(_mm512_xor_epi32(_mm512_castpd_si512(a), _mm512_castpd_si512(b)))
 #define gmx_simd_rsqrt_d(x)        _mm512_cvtpslo_pd(_mm512_rsqrt23_ps(_mm512_cvtpd_pslo(x)))
 #define gmx_simd_rcp_d(x)          _mm512_cvtpslo_pd(_mm512_rcp23_ps(_mm512_cvtpd_pslo(x)))
-#define gmx_simd_fabs_d(x)         gmx_simd_andnot_d(_mm512_set1_pd(-0.0), x)
+#define gmx_simd_fabs_d(x)         gmx_simd_andnot_d(_mm512_set1_pd(GMX_DOUBLE_NEGZERO), x)
 #define gmx_simd_fneg_d(x)         _mm512_addn_pd(x, _mm512_setzero_pd())
 #define gmx_simd_max_d             _mm512_gmax_pd
 #define gmx_simd_min_d             _mm512_gmin_pd
@@ -282,7 +282,7 @@
 #define gmx_simd4_or_f(a, b)        _mm512_castsi512_ps(_mm512_mask_or_epi32(_mm512_undefined_epi32(), gmx_simd4_mask, _mm512_castps_si512(a), _mm512_castps_si512(b)))
 #define gmx_simd4_xor_f(a, b)       _mm512_castsi512_ps(_mm512_mask_xor_epi32(_mm512_undefined_epi32(), gmx_simd4_mask, _mm512_castps_si512(a), _mm512_castps_si512(b)))
 #define gmx_simd4_rsqrt_f(a)        _mm512_mask_rsqrt23_ps(_mm512_undefined_ps(), gmx_simd4_mask, a)
-#define gmx_simd4_fabs_f(x)         gmx_simd4_andnot_f(_mm512_set1_ps(-0.0), x)
+#define gmx_simd4_fabs_f(x)         gmx_simd4_andnot_f(_mm512_set1_ps(GMX_FLOAT_NEGZERO), x)
 #define gmx_simd4_fneg_f(x)         _mm512_mask_addn_ps(_mm512_undefined_ps(), gmx_simd4_mask, x, _mm512_setzero_ps())
 #define gmx_simd4_max_f(a, b)       _mm512_mask_gmax_ps(_mm512_undefined_ps(), gmx_simd4_mask, a, b)
 #define gmx_simd4_min_f(a, b)       _mm512_mask_gmin_ps(_mm512_undefined_ps(), gmx_simd4_mask, a, b)
@@ -325,7 +325,7 @@
 #define gmx_simd4_or_d(a, b)        _mm512_castsi512_pd(_mm512_mask_or_epi32(_mm512_undefined_epi32(), mask_loh, _mm512_castpd_si512(a), _mm512_castpd_si512(b)))
 #define gmx_simd4_xor_d(a, b)       _mm512_castsi512_pd(_mm512_mask_xor_epi32(_mm512_undefined_epi32(), mask_loh, _mm512_castpd_si512(a), _mm512_castpd_si512(b)))
 #define gmx_simd4_rsqrt_d(a)        _mm512_mask_cvtpslo_pd(_mm512_undefined_pd(), gmx_simd4_mask, _mm512_mask_rsqrt23_ps(_mm512_undefined_ps(), gmx_simd4_mask, _mm512_mask_cvtpd_pslo(_mm512_undefined_ps(), gmx_simd4_mask, x)))
-#define gmx_simd4_fabs_d(x)         gmx_simd4_andnot_d(_mm512_set1_pd(-0.0), x)
+#define gmx_simd4_fabs_d(x)         gmx_simd4_andnot_d(_mm512_set1_pd(GMX_DOUBLE_NEGZERO), x)
 #define gmx_simd4_fneg_d(x)         _mm512_mask_addn_pd(_mm512_undefined_pd(), gmx_simd4_mask, x, _mm512_setzero_pd())
 #define gmx_simd4_max_d(a, b)       _mm512_mask_gmax_pd(_mm512_undefined_pd(), gmx_simd4_mask, a, b)
 #define gmx_simd4_min_d(a, b)       _mm512_mask_gmin_pd(_mm512_undefined_pd(), gmx_simd4_mask, a, b)

diff --git a/src/gromacs/simd/impl_x86_avx_128_fma/impl_x86_avx_128_fma.h b/src/gromacs/simd/impl_x86_avx_128_fma/impl_x86_avx_128_fma.h
index 823bfe81b996ef2aaefbfce38b1791c5b8ed6785..5b3096bee322f5fe367c39da2165a030ea6b1db7 100644 (file)
--- a/src/gromacs/simd/impl_x86_avx_128_fma/impl_x86_avx_128_fma.h
+++ b/src/gromacs/simd/impl_x86_avx_128_fma/impl_x86_avx_128_fma.h
@@ -104,8 +104,8 @@
 #define gmx_simd4_or_d                   _mm256_or_pd
 #define gmx_simd4_xor_d                  _mm256_xor_pd
 #define gmx_simd4_rsqrt_d(x)             _mm256_cvtps_pd(_mm_rsqrt_ps(_mm256_cvtpd_ps(x)))
-#define gmx_simd4_fabs_d(x)              _mm256_andnot_pd(_mm256_set1_pd(-0.0), x)
-#define gmx_simd4_fneg_d(x)              _mm256_xor_pd(x, _mm256_set1_pd(-0.0))
+#define gmx_simd4_fabs_d(x)              _mm256_andnot_pd(_mm256_set1_pd(GMX_DOUBLE_NEGZERO), x)
+#define gmx_simd4_fneg_d(x)              _mm256_xor_pd(x, _mm256_set1_pd(GMX_DOUBLE_NEGZERO))
 #define gmx_simd4_max_d                  _mm256_max_pd
 #define gmx_simd4_min_d                  _mm256_min_pd
 #define gmx_simd4_round_d(x)             _mm256_round_pd(x, _MM_FROUND_NINT)

diff --git a/src/gromacs/simd/impl_x86_avx_256/impl_x86_avx_256.h b/src/gromacs/simd/impl_x86_avx_256/impl_x86_avx_256.h
index d787708b4c0f6e44cd68ed55b727f8190774a02b..cff1a7e2cbd00bb782aadfba2b862214706a98d1 100644 (file)
--- a/src/gromacs/simd/impl_x86_avx_256/impl_x86_avx_256.h
+++ b/src/gromacs/simd/impl_x86_avx_256/impl_x86_avx_256.h
@@ -105,8 +105,8 @@
 #define gmx_simd_xor_f             _mm256_xor_ps
 #define gmx_simd_rsqrt_f           _mm256_rsqrt_ps
 #define gmx_simd_rcp_f             _mm256_rcp_ps
-#define gmx_simd_fabs_f(x)         _mm256_andnot_ps(_mm256_set1_ps(-0.0), x)
-#define gmx_simd_fneg_f(x)         _mm256_xor_ps(x, _mm256_set1_ps(-0.0))
+#define gmx_simd_fabs_f(x)         _mm256_andnot_ps(_mm256_set1_ps(GMX_FLOAT_NEGZERO), x)
+#define gmx_simd_fneg_f(x)         _mm256_xor_ps(x, _mm256_set1_ps(GMX_FLOAT_NEGZERO))
 #define gmx_simd_max_f             _mm256_max_ps
 #define gmx_simd_min_f             _mm256_min_ps
 #define gmx_simd_round_f(x)        _mm256_round_ps(x, _MM_FROUND_NINT)

diff --git a/src/gromacs/simd/impl_x86_sse2/impl_x86_sse2.h b/src/gromacs/simd/impl_x86_sse2/impl_x86_sse2.h
index 5d6b195965b25441f3bc1ca030dbfe6d51dd4b98..7aab27ae21c5faad2de33dde08b39594b00498e8 100644 (file)
--- a/src/gromacs/simd/impl_x86_sse2/impl_x86_sse2.h
+++ b/src/gromacs/simd/impl_x86_sse2/impl_x86_sse2.h
@@ -99,8 +99,8 @@
 #define gmx_simd_xor_f            _mm_xor_ps
 #define gmx_simd_rsqrt_f          _mm_rsqrt_ps
 #define gmx_simd_rcp_f            _mm_rcp_ps
-#define gmx_simd_fabs_f(x)        _mm_andnot_ps(_mm_set1_ps(-0.0), x)
-#define gmx_simd_fneg_f(x)        _mm_xor_ps(x, _mm_set1_ps(-0.0))
+#define gmx_simd_fabs_f(x)        _mm_andnot_ps(_mm_set1_ps(GMX_FLOAT_NEGZERO), x)
+#define gmx_simd_fneg_f(x)        _mm_xor_ps(x, _mm_set1_ps(GMX_FLOAT_NEGZERO))
 #define gmx_simd_max_f            _mm_max_ps
 #define gmx_simd_min_f            _mm_min_ps
 #define gmx_simd_round_f(x)       _mm_cvtepi32_ps(_mm_cvtps_epi32(x))
@@ -183,8 +183,8 @@
 #define gmx_simd_rsqrt_d(x)        _mm_cvtps_pd(_mm_rsqrt_ps(_mm_cvtpd_ps(x)))
 /* Don't use FMA for sqrt N-R iterations - this saves 1 instruction without FMA hardware */
 #define gmx_simd_rcp_d(x)          _mm_cvtps_pd(_mm_rcp_ps(_mm_cvtpd_ps(x)))
-#define gmx_simd_fabs_d(x)         _mm_andnot_pd(_mm_set1_pd(-0.0), x)
-#define gmx_simd_fneg_d(x)         _mm_xor_pd(x, _mm_set1_pd(-0.0))
+#define gmx_simd_fabs_d(x)         _mm_andnot_pd(_mm_set1_pd(GMX_DOUBLE_NEGZERO), x)
+#define gmx_simd_fneg_d(x)         _mm_xor_pd(x, _mm_set1_pd(GMX_DOUBLE_NEGZERO))
 #define gmx_simd_max_d             _mm_max_pd
 #define gmx_simd_min_d             _mm_min_pd
 #define gmx_simd_round_d(x)        _mm_cvtepi32_pd(_mm_cvtpd_epi32(x))

diff --git a/src/gromacs/simd/simd_math.h b/src/gromacs/simd/simd_math.h
index 1f6dc08361ade3a6ee3c77a1cba1c839b10c9a2a..68ab6774ef0031b3f4b71ca5cceb21663245c59f 100644 (file)
--- a/src/gromacs/simd/simd_math.h
+++ b/src/gromacs/simd/simd_math.h
@@ -124,7 +124,7 @@ static gmx_inline gmx_simd_float_t gmx_simdcall
 gmx_simd_xor_sign_f(gmx_simd_float_t a, gmx_simd_float_t b)
 {
 #ifdef GMX_SIMD_HAVE_LOGICAL
-    return gmx_simd_xor_f(a, gmx_simd_and_f(gmx_simd_set1_f(-0.0), b));
+    return gmx_simd_xor_f(a, gmx_simd_and_f(gmx_simd_set1_f(GMX_FLOAT_NEGZERO), b));
 #else
     return gmx_simd_blendv_f(a, gmx_simd_fneg_f(a), gmx_simd_cmplt_f(b, gmx_simd_setzero_f()));
 #endif
@@ -729,8 +729,8 @@ gmx_simd_sincos_f(gmx_simd_float_t x, gmx_simd_float_t *sinval, gmx_simd_float_t
     y       = gmx_simd_round_f(z);
 
     mask    = gmx_simd_cvt_fib2fb(gmx_simd_cmpeq_fi(gmx_simd_and_fi(iy, ione), gmx_simd_setzero_fi()));
-    ssign   = gmx_simd_blendzero_f(gmx_simd_set1_f(-0.0f), gmx_simd_cvt_fib2fb(gmx_simd_cmpeq_fi(gmx_simd_and_fi(iy, itwo), itwo)));
-    csign   = gmx_simd_blendzero_f(gmx_simd_set1_f(-0.0f), gmx_simd_cvt_fib2fb(gmx_simd_cmpeq_fi(gmx_simd_and_fi(gmx_simd_add_fi(iy, ione), itwo), itwo)));
+    ssign   = gmx_simd_blendzero_f(gmx_simd_set1_f(GMX_FLOAT_NEGZERO), gmx_simd_cvt_fib2fb(gmx_simd_cmpeq_fi(gmx_simd_and_fi(iy, itwo), itwo)));
+    csign   = gmx_simd_blendzero_f(gmx_simd_set1_f(GMX_FLOAT_NEGZERO), gmx_simd_cvt_fib2fb(gmx_simd_cmpeq_fi(gmx_simd_and_fi(gmx_simd_add_fi(iy, ione), itwo), itwo)));
 #else
     const gmx_simd_float_t  quarter         = gmx_simd_set1_f(0.25f);
     const gmx_simd_float_t  minusquarter    = gmx_simd_set1_f(-0.25f);
@@ -766,8 +766,8 @@ gmx_simd_sincos_f(gmx_simd_float_t x, gmx_simd_float_t *sinval, gmx_simd_float_t
      * active or inactive - you will get errors if only one is used.
      */
 #    ifdef GMX_SIMD_HAVE_LOGICAL
-    ssign   = gmx_simd_and_f(ssign, gmx_simd_set1_f(-0.0f));
-    csign   = gmx_simd_andnot_f(q, gmx_simd_set1_f(-0.0f));
+    ssign   = gmx_simd_and_f(ssign, gmx_simd_set1_f(GMX_FLOAT_NEGZERO));
+    csign   = gmx_simd_andnot_f(q, gmx_simd_set1_f(GMX_FLOAT_NEGZERO));
     ssign   = gmx_simd_xor_f(ssign, csign);
 #    else
     csign   = gmx_simd_xor_sign_f(gmx_simd_set1_f(-1.0f), q);
@@ -884,7 +884,7 @@ gmx_simd_tan_f(gmx_simd_float_t x)
     x       = gmx_simd_fnmadd_f(y, argred1, x);
     x       = gmx_simd_fnmadd_f(y, argred2, x);
     x       = gmx_simd_fnmadd_f(y, argred3, x);
-    x       = gmx_simd_xor_f(gmx_simd_blendzero_f(gmx_simd_set1_f(-0.0f), mask), x);
+    x       = gmx_simd_xor_f(gmx_simd_blendzero_f(gmx_simd_set1_f(GMX_FLOAT_NEGZERO), mask), x);
 #else
     const gmx_simd_float_t  quarter         = gmx_simd_set1_f(0.25f);
     const gmx_simd_float_t  half            = gmx_simd_set1_f(0.5f);
@@ -1338,7 +1338,7 @@ static gmx_inline gmx_simd_double_t gmx_simdcall
 gmx_simd_xor_sign_d(gmx_simd_double_t a, gmx_simd_double_t b)
 {
 #ifdef GMX_SIMD_HAVE_LOGICAL
-    return gmx_simd_xor_d(a, gmx_simd_and_d(gmx_simd_set1_d(-0.0), b));
+    return gmx_simd_xor_d(a, gmx_simd_and_d(gmx_simd_set1_d(GMX_DOUBLE_NEGZERO), b));
 #else
     return gmx_simd_blendv_d(a, gmx_simd_fneg_d(a), gmx_simd_cmplt_d(b, gmx_simd_setzero_d()));
 #endif
@@ -2025,8 +2025,8 @@ gmx_simd_sincos_d(gmx_simd_double_t x, gmx_simd_double_t *sinval, gmx_simd_doubl
     y       = gmx_simd_round_d(z);
 
     mask    = gmx_simd_cvt_dib2db(gmx_simd_cmpeq_di(gmx_simd_and_di(iy, ione), gmx_simd_setzero_di()));
-    ssign   = gmx_simd_blendzero_d(gmx_simd_set1_d(-0.0), gmx_simd_cvt_dib2db(gmx_simd_cmpeq_di(gmx_simd_and_di(iy, itwo), itwo)));
-    csign   = gmx_simd_blendzero_d(gmx_simd_set1_d(-0.0), gmx_simd_cvt_dib2db(gmx_simd_cmpeq_di(gmx_simd_and_di(gmx_simd_add_di(iy, ione), itwo), itwo)));
+    ssign   = gmx_simd_blendzero_d(gmx_simd_set1_d(GMX_DOUBLE_NEGZERO), gmx_simd_cvt_dib2db(gmx_simd_cmpeq_di(gmx_simd_and_di(iy, itwo), itwo)));
+    csign   = gmx_simd_blendzero_d(gmx_simd_set1_d(GMX_DOUBLE_NEGZERO), gmx_simd_cvt_dib2db(gmx_simd_cmpeq_di(gmx_simd_and_di(gmx_simd_add_di(iy, ione), itwo), itwo)));
 #else
     const gmx_simd_double_t  quarter         = gmx_simd_set1_d(0.25);
     const gmx_simd_double_t  minusquarter    = gmx_simd_set1_d(-0.25);
@@ -2062,8 +2062,8 @@ gmx_simd_sincos_d(gmx_simd_double_t x, gmx_simd_double_t *sinval, gmx_simd_doubl
      * active or inactive - you will get errors if only one is used.
      */
 #    ifdef GMX_SIMD_HAVE_LOGICAL
-    ssign   = gmx_simd_and_d(ssign, gmx_simd_set1_d(-0.0));
-    csign   = gmx_simd_andnot_d(q, gmx_simd_set1_d(-0.0));
+    ssign   = gmx_simd_and_d(ssign, gmx_simd_set1_d(GMX_DOUBLE_NEGZERO));
+    csign   = gmx_simd_andnot_d(q, gmx_simd_set1_d(GMX_DOUBLE_NEGZERO));
     ssign   = gmx_simd_xor_d(ssign, csign);
 #    else
     csign   = gmx_simd_xor_sign_d(gmx_simd_set1_d(-1.0), q);
@@ -2179,7 +2179,7 @@ gmx_simd_tan_d(gmx_simd_double_t x)
     x       = gmx_simd_fnmadd_d(y, argred1, x);
     x       = gmx_simd_fnmadd_d(y, argred2, x);
     x       = gmx_simd_fnmadd_d(y, argred3, x);
-    x       = gmx_simd_xor_d(gmx_simd_blendzero_d(gmx_simd_set1_d(-0.0), mask), x);
+    x       = gmx_simd_xor_d(gmx_simd_blendzero_d(gmx_simd_set1_d(GMX_DOUBLE_NEGZERO), mask), x);
 #else
     const gmx_simd_double_t  quarter         = gmx_simd_set1_d(0.25);
     const gmx_simd_double_t  half            = gmx_simd_set1_d(0.5);

diff --git a/src/testutils/tests/testasserts_tests.cpp b/src/testutils/tests/testasserts_tests.cpp
index 111bbc5e627bf0d2ee0aaf3fc7996fb155c1b317..c586374863360c74c40cde97fa39f94e6f6b9f7a 100644 (file)
--- a/src/testutils/tests/testasserts_tests.cpp
+++ b/src/testutils/tests/testasserts_tests.cpp
@@ -75,7 +75,7 @@ TEST(FloatingPointDifferenceTest, HandlesEqualValues)
 
 TEST(FloatingPointDifferenceTest, HandlesZerosOfDifferentSign)
 {
-    FloatingPointDifference diff(0.0, -0.0);
+    FloatingPointDifference diff(0.0, GMX_DOUBLE_NEGZERO);
     EXPECT_FALSE(diff.isNaN());
     EXPECT_EQ(0.0, diff.asAbsolute());
     EXPECT_EQ(0U,  diff.asUlps());
@@ -91,7 +91,7 @@ TEST(FloatingPointDifferenceTest, HandlesSignComparisonWithZero)
         EXPECT_TRUE(diff.signsDiffer());
     }
     {
-        FloatingPointDifference diff(-0.0, -1.2);
+        FloatingPointDifference diff(GMX_DOUBLE_NEGZERO, -1.2);
         EXPECT_FALSE(diff.isNaN());
         EXPECT_DOUBLE_EQ(1.2, diff.asAbsolute());
         EXPECT_FALSE(diff.signsDiffer());
@@ -120,7 +120,7 @@ TEST(FloatingPointDifferenceTest, HandlesUlpDifferences)
 
 TEST(FloatingPointDifferenceTest, HandlesUlpDifferenceAcrossZero)
 {
-    const double            first  = addUlps(-0.0, 2);
+    const double            first  = addUlps(GMX_DOUBLE_NEGZERO, 2);
     const double            second = addUlps( 0.0, 2);
     FloatingPointDifference diff(first, second);
     EXPECT_FALSE(diff.isNaN());