[libc-commits] [PATCH] D121839: [libc] Clean up Windows build

[Michael Jones via Phabricator via libc-commits]

michaelrj updated this revision to Diff 416004.
michaelrj added a comment.

fix the FE_DFL_ENV behavior for set_env


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D121839/new/

https://reviews.llvm.org/D121839

Files:
  libc/config/windows/entrypoints.txt
  libc/src/__support/FPUtil/x86_64/FEnvImpl.h


Index: libc/src/__support/FPUtil/x86_64/FEnvImpl.h
===================================================================
--- libc/src/__support/FPUtil/x86_64/FEnvImpl.h
+++ libc/src/__support/FPUtil/x86_64/FEnvImpl.h
@@ -345,8 +345,8 @@
 // MSVC fenv.h defines a very simple representation of the floating point state
 // which just consists of control and status words of the x87 unit.
 struct FPState {
-  uint32_t ControlWord;
-  uint32_t StatusWord;
+  uint32_t control_word;
+  uint32_t status_word;
 };
 #else
 struct FPState {
@@ -364,20 +364,51 @@
 #ifdef _WIN32
 static inline int get_env(fenv_t *envp) {
   internal::FPState *state = reinterpret_cast<internal::FPState *>(envp);
-  internal::X87StateDescriptor X87Status;
-  internal::getX87StateDescriptor(X87Status);
-  state->ControlWord = X87Status.ControlWord;
-  state->StatusWord = X87Status.StatusWord;
+  internal::X87StateDescriptor x87_status;
+  internal::get_x87_state_descriptor(x87_status);
+  state->control_word = x87_status.control_word;
+  state->status_word = x87_status.status_word;
   return 0;
 }
 
 static inline int set_env(const fenv_t *envp) {
   const internal::FPState *state =
       reinterpret_cast<const internal::FPState *>(envp);
-  internal::X87StateDescriptor X87Status;
-  X87Status.ControlWord = state->ControlWord;
-  X87Status.StatusWord = state->StatusWord;
-  internal::writeX87StateDescriptor(X87Status);
+  internal::X87StateDescriptor x87_status;
+
+  if (envp == FE_DFL_ENV) {
+    // Reset the exception flags in the status word.
+    x87_status.status_word &= ~uint16_t(0x3F);
+    // Reset other non-sensitive parts of the status word.
+    for (int i = 0; i < 5; i++)
+      x87_status._[i] = 0;
+    // In the control word, we do the following:
+    // 1. Mask all exceptions
+    // 2. Set rounding mode to round-to-nearest
+    // 3. Set the internal precision to double extended precision.
+    x87_status.control_word |= uint16_t(0x3F);         // Mask all exceptions.
+    x87_status.control_word &= ~(uint16_t(0x3) << 10); // Round to nearest.
+    x87_status.control_word |= (uint16_t(0x3) << 8);   // Extended precision.
+    internal::write_x87_state_descriptor(x87_status);
+
+    // We take the exact same approach MXCSR register as well.
+    // MXCSR has two additional fields, "flush-to-zero" and
+    // "denormals-are-zero". We reset those bits. Also, MXCSR does not
+    // have a field which controls the precision of internal operations.
+    uint32_t mxcsr = internal::get_mxcsr();
+    mxcsr &= ~uint16_t(0x3F);        // Clear exception flags.
+    mxcsr &= ~(uint16_t(0x1) << 6);  // Reset denormals-are-zero
+    mxcsr |= (uint16_t(0x3F) << 7);  // Mask exceptions
+    mxcsr &= ~(uint16_t(0x3) << 13); // Round to nearest.
+    mxcsr &= ~(uint16_t(0x1) << 15); // Reset flush-to-zero
+    internal::write_mxcsr(mxcsr);
+
+    return 0;
+  }
+
+  x87_status.control_word = state->control_word;
+  x87_status.status_word = state->status_word;
+  internal::write_x87_state_descriptor(x87_status);
   return 0;
 }
 #else
Index: libc/config/windows/entrypoints.txt
===================================================================
--- libc/config/windows/entrypoints.txt
+++ libc/config/windows/entrypoints.txt
@@ -17,9 +17,6 @@
     libc.src.ctype.tolower
     libc.src.ctype.toupper
 
-    # errno.h entrypoints
-    libc.src.errno.__errno_location
-
     # string.h entrypoints
     libc.src.string.bcmp
     libc.src.string.bzero


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