[PULL,052/115] target/i386: fix fscale handling of signaling NaN

Commit Message

Paolo Bonzini June 11, 2020, 7:43 p.m. UTC

From: Joseph Myers <[e-mail]>

The implementation of the fscale instruction returns a NaN exponent
unchanged.  Fix it to return a quiet NaN when the provided exponent is
a signaling NaN.

Signed-off-by: Joseph Myers <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>
---
 target/i386/fpu_helper.c          |  4 ++++
 tests/tcg/i386/test-i386-fscale.c | 37 +++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)
 create mode 100644 tests/tcg/i386/test-i386-fscale.c

Patch

diff --git a/target/i386/fpu_helper.c b/target/i386/fpu_helper.c
index 568bd3b359..0671de6952 100644
--- a/target/i386/fpu_helper.c
+++ b/target/i386/fpu_helper.c
@@ -970,6 +970,10 @@  void helper_fscale(CPUX86State *env)
 {
     if (floatx80_is_any_nan(ST1)) {
         ST0 = ST1;
+        if (floatx80_is_signaling_nan(ST0, &env->fp_status)) {
+            float_raise(float_flag_invalid, &env->fp_status);
+            ST0 = floatx80_silence_nan(ST0, &env->fp_status);
+        }
     } else {
         int n = floatx80_to_int32_round_to_zero(ST1, &env->fp_status);
         ST0 = floatx80_scalbn(ST0, n, &env->fp_status);
diff --git a/tests/tcg/i386/test-i386-fscale.c b/tests/tcg/i386/test-i386-fscale.c
new file mode 100644
index 0000000000..aecac5125f
--- /dev/null
+++ b/tests/tcg/i386/test-i386-fscale.c
@@ -0,0 +1,37 @@ 
+/* Test fscale instruction.  */
+
+#include <stdint.h>
+#include <stdio.h>
+
+union u {
+    struct { uint64_t sig; uint16_t sign_exp; } s;
+    long double ld;
+};
+
+volatile long double ld_res;
+
+int isnan_ld(long double x)
+{
+  union u tmp = { .ld = x };
+  return ((tmp.s.sign_exp & 0x7fff) == 0x7fff &&
+          (tmp.s.sig >> 63) != 0 &&
+          (tmp.s.sig << 1) != 0);
+}
+
+int issignaling_ld(long double x)
+{
+    union u tmp = { .ld = x };
+    return isnan_ld(x) && (tmp.s.sig & UINT64_C(0x4000000000000000)) == 0;
+}
+
+int main(void)
+{
+    int ret = 0;
+    __asm__ volatile ("fscale" : "=t" (ld_res) :
+                      "0" (2.5L), "u" (__builtin_nansl("")));
+    if (!isnan_ld(ld_res) || issignaling_ld(ld_res)) {
+        printf("FAIL: fscale snan\n");
+        ret = 1;
+    }
+    return ret;
+}