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authorDenis Vlasenko <vda.linux@googlemail.com>2009-02-08 02:04:10 +0000
committerDenis Vlasenko <vda.linux@googlemail.com>2009-02-08 02:04:10 +0000
commit7cccb9c2531088502492d92e8632159653de6290 (patch)
tree7e34bb6d1956204501b511c2532fd552cf407df2
parent49173d980edd36861fdb00830b8b63d9297327e6 (diff)
nextafterf: trying to correct FP exception handling
-rw-r--r--docs/probe_math_exception.c41
-rw-r--r--libm/math_private.h55
-rw-r--r--libm/s_nextafterf.c15
3 files changed, 100 insertions, 11 deletions
diff --git a/docs/probe_math_exception.c b/docs/probe_math_exception.c
new file mode 100644
index 000000000..dbeccc5cc
--- /dev/null
+++ b/docs/probe_math_exception.c
@@ -0,0 +1,41 @@
+/* Small test program for probing how various math functions
+ * with specific operands set floating point exceptions
+ */
+
+#define _ISOC99_SOURCE 1
+#define _GNU_SOURCE 1
+
+#include <math.h>
+#include <fenv.h>
+#include <stdio.h>
+
+int main(int argc, char **argv)
+{
+ float infF = HUGE_VALF * 2;
+
+ feclearexcept(FE_ALL_EXCEPT);
+
+// printf("%.40e\n", 1.0 / 0.0); // FE_DIVBYZERO
+// printf("%.40e\n", nextafterf(HUGE_VALF, infF)); // no exceptions in glibc 2.4
+
+#define PREX(ex) do { if (fetestexcept(ex)) printf(#ex); } while(0)
+#ifdef FE_INEXACT
+ PREX(FE_INEXACT);
+#endif
+#ifdef FE_DIVBYZERO
+ PREX(FE_DIVBYZERO);
+#endif
+#ifdef FE_UNDERFLOW
+ PREX(FE_UNDERFLOW);
+#endif
+#ifdef FE_OVERFLOW
+ PREX(FE_OVERFLOW);
+#endif
+#ifdef FE_INVALID
+ PREX(FE_INVALID);
+#endif
+ if (fetestexcept(FE_ALL_EXCEPT))
+ printf("\n");
+ printf("done\n");
+ return 0;
+}
diff --git a/libm/math_private.h b/libm/math_private.h
index bdd0aba48..0601f2c3d 100644
--- a/libm/math_private.h
+++ b/libm/math_private.h
@@ -187,4 +187,59 @@ extern double __kernel_cos (double,double) attribute_hidden;
extern double __kernel_tan (double,double,int) attribute_hidden;
extern int __kernel_rem_pio2 (double*,double*,int,int,int,const int*) attribute_hidden;
+/*
+ * math_opt_barrier(x): force expression x to be evaluated and put into
+ * a floating point register or memory. This macro returns the value.
+ *
+ * math_force_eval(x): force expression x to be evaluated and put into
+ * a floating point register or memory *of the appropriate size*.
+ * This forces floating point flags to be set correctly
+ * (for example, when float value is overflowing, but FPU registers
+ * are wide enough to "hide" this).
+ */
+#if defined(__i386__)
+#define math_opt_barrier(x) ({ \
+ __typeof(x) __x = (x); \
+ /* "t": load x into top-of-stack fpreg */ \
+ __asm ("" : "=t" (__x) : "0" (__x)); \
+ __x; \
+})
+#define math_force_eval(x) do { \
+ if (sizeof(x) <= sizeof(double)) \
+ /* "m": store x into a memory location */ \
+ __asm __volatile ("" : : "m" (x)); \
+ else /* long double */ \
+ /* "f": load x into (any) fpreg */ \
+ __asm __volatile ("" : : "f" (x)); \
+} while (0)
+#endif
+
+#if defined(__x86_64__)
+#define math_opt_barrier(x) ({ \
+ __typeof(x) __x = (x); \
+ if (sizeof(x) <= sizeof(double)) \
+ /* "x": load into XMM SSE register */ \
+ __asm ("" : "=x" (__x) : "0" (__x)); \
+ else /* long double */ \
+ /* "t": load x into top-of-stack fpreg */ \
+ __asm ("" : "=t" (__x) : "0" (__x)); \
+ __x; \
+})
+#define math_force_eval(x) do { \
+ if (sizeof(x) <= sizeof(double)) \
+ /* "x": load into XMM SSE register */ \
+ __asm __volatile ("" : : "x" (x)); \
+ else /* long double */ \
+ /* "f": load x into (any) fpreg */ \
+ __asm __volatile ("" : : "f" (x)); \
+} while (0)
+#endif
+
+/* Default implementation forces store to a memory location */
+#ifndef math_opt_barrier
+#define math_opt_barrier(x) ({ __typeof(x) __x = (x); __asm ("" : "+m" (__x)); __x; })
+#define math_force_eval(x) __asm __volatile ("" : : "m" (x))
+#endif
+
+
#endif /* _MATH_PRIVATE_H_ */
diff --git a/libm/s_nextafterf.c b/libm/s_nextafterf.c
index 8dee00ff7..5fc44e31c 100644
--- a/libm/s_nextafterf.c
+++ b/libm/s_nextafterf.c
@@ -16,11 +16,6 @@
#include "math.h"
#include "math_private.h"
-#ifndef math_opt_barrier
-# define math_opt_barrier(x) ({ __typeof (x) __x = x; __asm ("" : "+m" (__x)); __x; })
-# define math_force_eval(x) __asm __volatile ("" : : "m" (x))
-#endif
-
float nextafterf(float x, float y)
{
int32_t hx, hy, ix, iy;
@@ -38,12 +33,12 @@ float nextafterf(float x, float y)
return y;
if (ix == 0) { /* x == 0? */
- float u;
+// glibc 2.4 does not seem to set underflow?
+// float u;
/* return +-minsubnormal */
SET_FLOAT_WORD(x, (hy & 0x80000000) | 1);
- u = math_opt_barrier(x);
- u = u * u;
- math_force_eval(u); /* raise underflow flag */
+// u = x * x; /* raise underflow flag */
+// math_force_eval(u);
return x;
}
@@ -63,8 +58,6 @@ float nextafterf(float x, float y)
hy = hx & 0x7f800000;
if (hy >= 0x7f800000) {
x = x + x; /* overflow */
-//?? if (FLT_EVAL_METHOD != 0)
-// asm ("" : "+m"(x));
return x; /* overflow */
}
if (hy < 0x00800000) {