Fixing an error in PAL_pow that caused it to return an incorrect value for a couple scenarios. (#5399)

* Fixing an error in PAL_pow that caused it to return an incorrect value for a couple scenarios.

* Adding additional PAL_pow tests.

3 files changed, 70 insertions, 21 deletions

diff --git a/src/pal/src/configure.cmake b/src/pal/src/configure.cmake
index 4f1aabdbe6..24ed60e151 100644
--- a/src/pal/src/configure.cmake
+++ b/src/pal/src/configure.cmake
@@ -775,7 +775,25 @@ check_cxx_source_runs("
 
 int main(void) {
   double infinity = 1.0 / 0.0;
-  if (!isnan(pow(1.0, infinity))) {
+  if (pow(1.0, infinity) != 1.0 || pow(1.0, -infinity) != 1.0) {
+    exit(1)
+  }
+  if (!isnan(pow(-1.0, infinity)) || !isnan(pow(-1.0, -infinity))) {
+    exit(1);
+  }
+  if (pow(0.0, infinity) != 0.0) {
+    exit(1);
+  }
+  if (pow(0.0, -infinity) != infinity) {
+    exit(1);
+  }
+  if (pow(-1.1, infinity) != infinity || pow(1.1, infinity) != infinity) {
+    exit(1);
+  }
+  if (pow(-1.1, -infinity) != 0.0 || pow(1.1, infinity) != 0.0) {
+    exit(1);
+  }
+  if (pow(-0.0, -1) != -infinity) {
     exit(1);
   }
   if (pow(0.0, -1) != infinity) {
diff --git a/src/pal/src/cruntime/math.cpp b/src/pal/src/cruntime/math.cpp
index dd45110d2f..7075fd60f9 100644
--- a/src/pal/src/cruntime/math.cpp
+++ b/src/pal/src/cruntime/math.cpp
@@ -33,6 +33,8 @@ Abstract:
 #define PAL_POSINF_DBL -log(0.0)
 #define PAL_NEGINF_DBL  log(0.0)
 
+#define IS_DBL_NEGZERO(x)         (((*((INT64*)((void*)&x))) & I64(0xFFFFFFFFFFFFFFFF)) == I64(0x8000000000000000))
+
 SET_DEFAULT_DEBUG_CHANNEL(CRT);
 
 /*++
@@ -331,9 +333,13 @@ PALIMPORT double __cdecl PAL_pow(double x, double y)
     ENTRY("pow (x=%f, y=%f)\n", x, y);
 
 #if !HAVE_COMPATIBLE_POW
-    if (y == PAL_POSINF_DBL && !isnan(x))    // +Inf
+    if ((y == PAL_POSINF_DBL) && !isnan(x))    // +Inf
     {
-        if ((x == 1.0) || (x == -1.0))
+        if (x == 1.0)
+        {
+            ret = x;
+        }
+        else if (x == -1.0)
         {
             ret = PAL_NAN_DBL;    // NaN
         }
@@ -348,7 +354,11 @@ PALIMPORT double __cdecl PAL_pow(double x, double y)
     }
     else if ((y == PAL_NEGINF_DBL) && !isnan(x))   // -Inf
     {
-        if ((x == 1.0) || (x == -1.0))
+        if (x == 1.0)
+        {
+            ret = x;
+        }
+        else if (x == -1.0)
         {
             ret = PAL_NAN_DBL;    // NaN
         }
@@ -361,6 +371,10 @@ PALIMPORT double __cdecl PAL_pow(double x, double y)
             ret = 0.0;
         }
     }
+    else if (IS_DBL_NEGZERO(x) && (y == -1.0))
+    {
+        ret = PAL_NEGINF_DBL;    // -Inf
+    }
     else if ((x == 0.0) && (y < 0.0))
     {
         ret = PAL_POSINF_DBL;    // +Inf
@@ -377,9 +391,9 @@ PALIMPORT double __cdecl PAL_pow(double x, double y)
     }
     else
     {
-      ret = pow(x, y);
+        ret = pow(x, y);
     }
-    
+
 #if !HAVE_VALID_NEGATIVE_INF_POW
     if ((ret == PAL_POSINF_DBL) && (x < 0) && isfinite(x) && (ceil(y / 2) != floor(y / 2)))
     {
diff --git a/src/pal/tests/palsuite/c_runtime/pow/test1/test1.c b/src/pal/tests/palsuite/c_runtime/pow/test1/test1.c
index 690ae947ac..0a05cd5a47 100644
--- a/src/pal/tests/palsuite/c_runtime/pow/test1/test1.c
+++ b/src/pal/tests/palsuite/c_runtime/pow/test1/test1.c
@@ -91,26 +91,37 @@ int __cdecl main(int argc, char **argv)
     struct test tests[] = 
     {
         /* x                       y                       expected                   variance */
-        { PAL_NEGINF,              PAL_NEGINF,             0,                         PAL_EPSILON },
-        { PAL_NEGINF,              PAL_POSINF,             PAL_POSINF,                0 },
-
-        {  -10,                    PAL_NEGINF,             0,                         PAL_EPSILON },
-        {  -10,                   -1,                     -0.1,                       PAL_EPSILON },
-        {  -10,                    0,                      1,                         PAL_EPSILON * 10 },
-        {  -10,                    1,                     -10,                        PAL_EPSILON * 100 },
-        {  -10,                    PAL_POSINF,             PAL_POSINF,                0 },
-
-        {  -2.7182818284590452,    PAL_NEGINF,             0,                         PAL_EPSILON },          // x: -(e)
-        {  -2.7182818284590452,   -1,                     -0.36787944117144232,       PAL_EPSILON },          // x: -(e)
-        {  -2.7182818284590452,    0,                      1,                         PAL_EPSILON * 10 },     // x: -(e)
-        {  -2.7182818284590452,    1,                     -2.7182818284590452,        PAL_EPSILON * 10 },     // x: -(e)                       expected: e
-        {  -2.7182818284590452,    PAL_POSINF,             PAL_POSINF,                0 },                    // x: -(e)
-        
+        {  PAL_NEGINF,             PAL_NEGINF,             0,                         PAL_EPSILON },
+        {  PAL_NEGINF,             PAL_POSINF,             PAL_POSINF,                0 },
+
+        { -10,                     PAL_NEGINF,             0,                         PAL_EPSILON },
+        { -10,                    -1,                     -0.1,                       PAL_EPSILON },
+        { -10,                     0,                      1,                         PAL_EPSILON * 10 },
+        { -10,                     1,                     -10,                        PAL_EPSILON * 100 },
+        { -10,                     PAL_POSINF,             PAL_POSINF,                0 },
+
+        { -2.7182818284590452,     PAL_NEGINF,             0,                         PAL_EPSILON },          // x: -(e)
+        { -2.7182818284590452,    -1,                     -0.36787944117144232,       PAL_EPSILON },          // x: -(e)
+        { -2.7182818284590452,     0,                      1,                         PAL_EPSILON * 10 },     // x: -(e)
+        { -2.7182818284590452,     1,                     -2.7182818284590452,        PAL_EPSILON * 10 },     // x: -(e)                       expected: e
+        { -2.7182818284590452,     PAL_POSINF,             PAL_POSINF,                0 },                    // x: -(e)
+
+        { -0.0,                    PAL_NEGINF,             PAL_POSINF,                0 },
+        { -0.0,                   -1,                      PAL_NEGINF,                0 },
         { -0.0,                   -0.0,                    1,                         PAL_EPSILON * 10 },
         { -0.0,                    0,                      1,                         PAL_EPSILON * 10 },
+        { -0.0,                    1,                     -0.0,                       PAL_EPSILON },
+        { -0.0,                    PAL_POSINF,             0,                         PAL_EPSILON },
 
+        {  0.0,                    PAL_NEGINF,             PAL_POSINF,                0 },
+        {  0.0,                   -1,                      PAL_POSINF,                0 },
         {  0,                     -0.0,                    1,                         PAL_EPSILON * 10 },
         {  0,                      0,                      1,                         PAL_EPSILON * 10 },
+        {  0.0,                    1,                      0,                         PAL_EPSILON },
+        {  0.0,                    PAL_POSINF,             0,                         PAL_EPSILON },
+
+        {  1,                      PAL_NEGINF,             1,                         PAL_EPSILON * 10 },
+        {  1,                      PAL_POSINF,             1,                         PAL_EPSILON * 10 },
 
         {  2.7182818284590452,     PAL_NEGINF,             0,                         PAL_EPSILON },
         {  2.7182818284590452,    -3.1415926535897932,     0.043213918263772250,      PAL_EPSILON / 10 },     // x: e     y: -(pi)
@@ -199,6 +210,12 @@ int __cdecl main(int argc, char **argv)
     validate_isnan(-2.7182818284590452, -0.78539816339744828);                                                // x: -(e)  y: -(pi / 4)
     validate_isnan(-2.7182818284590452,  0.78539816339744828);                                                // x: -(e)  y:   pi / 4
     validate_isnan(-2.7182818284590452,  1.5707963267948966);                                                 // x: -(e)  y:   pi / 2
+
+    validate_isnan(-1, PAL_NEGINF);
+    validate_isnan(-1, PAL_POSINF);
+
+    validate_isnan(PAL_NAN, -0.0);
+    validate_isnan(PAL_NAN,  0);
     
     validate_isnan(PAL_NEGINF, PAL_NAN);
     validate_isnan(PAL_NAN,    PAL_NEGINF);