From e28c5496ebba30194cf110a5157e62e57af34406 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <campbell@mumble.net>
Date: Fri, 6 Aug 2010 01:18:01 +0000
Subject: [PATCH] Emulate C99 fenv.h on amd64 through the MXCSR.

---
 src/microcode/cmpauxmd/x86-64.m4 | 14 ++++++++++++++
 src/microcode/cmpintmd/x86-64.h  | 33 +++++++++++++++++++++++++++++++-
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/src/microcode/cmpauxmd/x86-64.m4 b/src/microcode/cmpauxmd/x86-64.m4
index fedb3e2ea..ff2238c57 100644
--- a/src/microcode/cmpauxmd/x86-64.m4
+++ b/src/microcode/cmpauxmd/x86-64.m4
@@ -966,6 +966,20 @@ asm_fixnum_rsh_overflow_negative:
 	OP(mov,q)	TW(IMM_DETAGGED_FIXNUM_MINUS_ONE,REG(rax))
 	ret
 
+define_c_label(x86_64_read_mxcsr)
+	enter		IMM(8),IMM(0)
+	stmxcsr		IND(REG(rsp))
+	OP(mov,l)	TW(IND(REG(rsp)),REG(eax))
+	leave
+	ret
+
+define_c_label(x86_64_write_mxcsr)
+	enter		IMM(8),IMM(0)
+	OP(mov,l)	TW(REG(eax),IND(REG(rsp)))
+	ldmxcsr		IND(REG(rsp))
+	leave
+	ret
+
 IFDASM(`end')
 
 # Mark the stack nonexecutable.  If we ever put code (e.g.,
diff --git a/src/microcode/cmpintmd/x86-64.h b/src/microcode/cmpintmd/x86-64.h
index 55090c953..d2e3bc55b 100644
--- a/src/microcode/cmpintmd/x86-64.h
+++ b/src/microcode/cmpintmd/x86-64.h
@@ -239,6 +239,37 @@ extern void asm_trampoline_to_interface (void);
 extern insn_t * read_compiled_closure_target (insn_t *);
 extern insn_t * read_uuo_target (SCHEME_OBJECT *);
 extern void x86_64_reset_hook (void);
-
+extern int x86_64_read_mxcsr (void);
+extern void x86_64_write_mxcsr (int);
+
+#ifndef HAVE_FENV_H
+
+#  define FE_TONEAREST 0
+#  define FE_DOWNWARD 1
+#  define FE_UPWARD 2
+#  define FE_TOWARDZERO 3
+
+#  define HAVE_FEGETROUND
+#  define HAVE_FESETROUND
+
+static inline int
+fegetround (void)
+{
+  return (3 & ((x86_64_read_mxcsr ()) >> 13));
+}
+
+static inline void
+fesetround (int mode)
+{
+  switch (mode)
+    {
+    case 0: case 1: case 2: case 3: break;
+    default: return (1);
+    }
+  x86_64_write_mxcsr ((mode << 13) | (0xffff9fff & (x86_64_read_mxcsr ())));
+  return (0);
+}
+
+#endif /* HAVE_FENV_H */
 
 #endif /* !SCM_CMPINTMD_H_INCLUDED */
-- 
2.25.1