LibC: Implement fenv.h

Userland/Libraries/LibC/CMakeLists.txt

@@ -6,6 +6,7 @@ set(LIBC_SOURCES
  dirent.cpp
  dlfcn.cpp
  fcntl.cpp
+ fenv.cpp
  getopt.cpp
  grp.cpp
  ioctl.cpp

Userland/Libraries/LibC/fenv.cpp

@@ -0,0 +1,229 @@
+/*
+ * Copyright (c) 2021, Mițca Dumitru <[email protected]>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ * list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/Types.h>
+#include <fenv.h>
+
+// This is the size of the floating point envinronment image in protected mode
+static_assert(sizeof(__x87_floating_point_environment) == 28);
+
+static u16 read_status_register()
+{
+ u16 status_register;
+ asm volatile("fstsw %0"
+ : "=m"(status_register));
+ return status_register;
+}
+
+static u16 read_control_word()
+{
+ u16 control_word;
+ asm volatile("fstcw %0"
+ : "=m"(control_word));
+ return control_word;
+}
+
+static void set_control_word(u16 new_control_word)
+{
+ asm volatile("fldcw %0" ::"m"(new_control_word));
+}
+
+static u32 read_mxcsr()
+{
+ u32 mxcsr;
+ asm volatile("stmxcsr %0"
+ : "=m"(mxcsr));
+ return mxcsr;
+}
+
+static void set_mxcsr(u32 new_mxcsr)
+{
+ asm volatile("ldmxcsr %0" ::"m"(new_mxcsr));
+}
+
+static constexpr u32 default_mxcsr_value = 0x1f80;
+
+extern "C" {
+
+int fegetenv(fenv_t* env)
+{
+ if (!env)
+ return 1;
+
+ asm volatile("fstenv %0"
+ : "=m"(env->__x87_fpu_env)::"memory");
+
+ env->__mxcsr = read_mxcsr();
+
+ return 0;
+}
+
+int fesetenv(const fenv_t* env)
+{
+ if (!env)
+ return 1;
+
+ if (env == FE_DFL_ENV) {
+ asm volatile("finit");
+ set_mxcsr(default_mxcsr_value);
+ return 0;
+ }
+
+ asm volatile("fldenv %0" ::"m"(env)
+ : "memory");
+
+ set_mxcsr(env->__mxcsr);
+
+ return 0;
+}
+
+int feholdexcept(fenv_t* env)
+{
+ fegetenv(env);
+
+ fenv_t current_env;
+ fegetenv(&current_env);
+
+ current_env.__x87_fpu_env.__status_word &= ~FE_ALL_EXCEPT;
+ current_env.__x87_fpu_env.__status_word &= ~(1 << 7); // Clear the "Exception Status Summary" bit
+ current_env.__x87_fpu_env.__control_word &= FE_ALL_EXCEPT; // Masking these bits stops the corresponding exceptions from being generated according to the Intel Programmer's Manual
+
+ fesetenv(&current_env);
+
+ return 0;
+}
+
+int feupdateenv(const fenv_t* env)
+{
+ auto currently_raised_exceptions = fetestexcept(FE_ALL_EXCEPT);
+
+ fesetenv(env);
+ feraiseexcept(currently_raised_exceptions);
+
+ return 0;
+}
+
+int fegetexceptflag(fexcept_t* except, int exceptions)
+{
+ if (!except)
+ return 1;
+ *except = (uint16_t)fetestexcept(exceptions);
+ return 0;
+}
+int fesetexceptflag(const fexcept_t* except, int exceptions)
+{
+ if (!except)
+ return 1;
+
+ fenv_t current_env;
+ fegetenv(&current_env);
+
+ exceptions &= FE_ALL_EXCEPT;
+ current_env.__x87_fpu_env.__status_word &= exceptions;
+ current_env.__x87_fpu_env.__status_word &= ~(1 << 7); // Make sure exceptions don't get raised
+
+ fesetenv(&current_env);
+ return 0;
+}
+
+int fegetround()
+{
+ // There's no way to signal whether the SSE rounding mode and x87 ones are different, so we assume they're the same
+ return (read_status_register() >> 10) & 3;
+}
+
+int fesetround(int rounding_mode)
+{
+ if (rounding_mode < FE_TONEAREST || rounding_mode > FE_TOWARDSZERO)
+ return 1;
+
+ auto control_word = read_control_word();
+
+ control_word &= ~(3 << 10);
+ control_word |= rounding_mode << 10;
+
+ set_control_word(control_word);
+
+ auto mxcsr = read_mxcsr();
+
+ mxcsr &= ~(3 << 13);
+ mxcsr |= rounding_mode << 13;
+
+ set_mxcsr(mxcsr);
+
+ return 0;
+}
+
+int feclearexcepts(int exceptions)
+{
+ exceptions &= FE_ALL_EXCEPT;
+
+ fenv_t current_env;
+ fegetenv(&current_env);
+
+ current_env.__x87_fpu_env.__status_word &= ~exceptions;
+ current_env.__x87_fpu_env.__status_word &= ~(1 << 7); // Clear the "Exception Status Summary" bit
+
+ fesetenv(&current_env);
+ return 0;
+}
+
+int fetestexcept(int exceptions)
+{
+ u16 status_register = read_status_register() & FE_ALL_EXCEPT;
+ exceptions &= FE_ALL_EXCEPT;
+
+ return status_register & exceptions;
+}
+
+int feraiseexcept(int exceptions)
+{
+ fenv_t env;
+ fegetenv(&env);
+
+ exceptions &= FE_ALL_EXCEPT;
+
+ // While the order in which the exceptions is raised is unspecified, FE_OVERFLOW and FE_UNDERFLOW must be raised before FE_INEXACT, so handle that case in this branch
+ if (exceptions & FE_INEXACT) {
+ env.__x87_fpu_env.__status_word &= ((u16)exceptions & ~FE_INEXACT);
+ fesetenv(&env);
+ asm volatile("fwait"); // "raise" the exception by performing a floating point operation
+
+ fegetenv(&env);
+ env.__x87_fpu_env.__status_word &= FE_INEXACT;
+ fesetenv(&env);
+ asm volatile("fwait");
+
+ return 0;
+ }
+
+ env.__x87_fpu_env.__status_word &= exceptions;
+ fesetenv(&env);
+ asm volatile("fwait");
+
+ return 0;
+}
+}

Userland/Libraries/LibC/fenv.h

@@ -0,0 +1,85 @@
+/*
+ * Copyright (c) 2021, Mițca Dumitru <[email protected]>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ * list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+struct __x87_floating_point_environment {
+ uint16_t __control_word;
+ uint16_t __reserved1;
+ uint16_t __status_word;
+ uint16_t __reserved2;
+ uint16_t __tag_word;
+ uint16_t __reserved3;
+ uint32_t __fpu_ip_offset;
+ uint16_t __fpu_ip_selector;
+ uint16_t __opcode : 11;
+ uint16_t __reserved4 : 5;
+ uint32_t __fpu_data_offset;
+ uint16_t __fpu_data_selector;
+ uint16_t __reserved5;
+};
+
+typedef struct fenv_t {
+ struct __x87_floating_point_environment __x87_fpu_env;
+ uint32_t __mxcsr;
+} fenv_t;
+
+#define FE_DFL_ENV ((const fenv_t*)-1)
+
+int fegetenv(fenv_t*);
+int fesetenv(const fenv_t*);
+int feholdexcept(fenv_t*);
+int feupdateenv(const fenv_t*);
+
+#define FE_INVALID 1u << 0
+#define FE_DIVBYZERO 1u << 2
+#define FE_OVERFLOW 1u << 3
+#define FE_UNDERFLOW 1u << 4
+#define FE_INEXACT 1u << 5
+#define FE_ALL_EXCEPT (FE_DIVBYZERO | FE_INEXACT | FE_INVALID | FE_OVERFLOW | FE_UNDERFLOW)
+
+typedef uint16_t fexcept_t;
+int fegetexceptflag(fexcept_t*, int exceptions);
+int fesetexceptflag(const fexcept_t*, int exceptions);
+
+int feclearexcepts(int exceptions);
+int fetestexcept(int exceptions);
+int feraiseexcept(int exceptions);
+
+#define FE_TONEAREST 0
+#define FE_DOWNWARD 1
+#define FE_UPWARD 2
+#define FE_TOWARDSZERO 3
+
+int fesetround(int round);
+int fegetround(void);
+
+__END_DECLS