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bh=6DTxtOc5LdYdP17d4UDiZN2OUZYIKMNt5E0uvZNLm+g=; b=godjkGweT2sWc3ak0rBpVyK0QBtdgJK22UByJXTn34oo6XmuImJ4oNAF8tzcq+AkWAJI56 LVXRqOhTnDQz/k+9MNTN31tjohZCRIw9oSaBaib4vL74nGoKmneZXEFIneDlQ9nv/l/nct tKTp91ve1+YKNckcd9duBCWc/NyOMoo= X-MC-Unique: IYNd9nSgOUatmNfMtw6ZlA-1 From: Paolo Bonzini To: qemu-devel@nongnu.org Subject: [PULL 054/115] target/i386: fix fscale handling of infinite exponents Date: Thu, 11 Jun 2020 15:43:48 -0400 Message-Id: <20200611194449.31468-55-pbonzini@redhat.com> In-Reply-To: <20200611194449.31468-1-pbonzini@redhat.com> References: <20200611194449.31468-1-pbonzini@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=207.211.31.120; envelope-from=pbonzini@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/11 08:37:10 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Joseph Myers Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: pass (identity @redhat.com) Content-Type: text/plain; charset="utf-8" From: Joseph Myers The fscale implementation passes infinite exponents through to generic code that rounds the exponent to a 32-bit integer before using floatx80_scalbn. In round-to-nearest mode, and ignoring exceptions, this works in many cases. But it fails to handle the special cases of scaling 0 by a +Inf exponent or an infinity by a -Inf exponent, which should produce a NaN, and because it produces an inexact result for finite nonzero numbers being scaled, the result is sometimes incorrect in other rounding modes. Add appropriate handling of infinite exponents to produce a NaN or an appropriately signed exact zero or infinity as a result. Signed-off-by: Joseph Myers Message-Id: Signed-off-by: Paolo Bonzini --- target/i386/fpu_helper.c | 22 ++++++++++++++++++++++ tests/tcg/i386/test-i386-fscale.c | 29 +++++++++++++++++++++++++++++ 2 files changed, 51 insertions(+) diff --git a/target/i386/fpu_helper.c b/target/i386/fpu_helper.c index 10ff90370e..72d1e77eb0 100644 --- a/target/i386/fpu_helper.c +++ b/target/i386/fpu_helper.c @@ -977,6 +977,28 @@ void helper_fscale(CPUX86State *env) float_raise(float_flag_invalid, &env->fp_status); ST0 =3D floatx80_silence_nan(ST0, &env->fp_status); } + } else if (floatx80_is_infinity(ST1) && + !floatx80_invalid_encoding(ST0) && + !floatx80_is_any_nan(ST0)) { + if (floatx80_is_neg(ST1)) { + if (floatx80_is_infinity(ST0)) { + float_raise(float_flag_invalid, &env->fp_status); + ST0 =3D floatx80_default_nan(&env->fp_status); + } else { + ST0 =3D (floatx80_is_neg(ST0) ? + floatx80_chs(floatx80_zero) : + floatx80_zero); + } + } else { + if (floatx80_is_zero(ST0)) { + float_raise(float_flag_invalid, &env->fp_status); + ST0 =3D floatx80_default_nan(&env->fp_status); + } else { + ST0 =3D (floatx80_is_neg(ST0) ? + floatx80_chs(floatx80_infinity) : + floatx80_infinity); + } + } } else { int n =3D floatx80_to_int32_round_to_zero(ST1, &env->fp_status); ST0 =3D floatx80_scalbn(ST0, n, &env->fp_status); diff --git a/tests/tcg/i386/test-i386-fscale.c b/tests/tcg/i386/test-i386-f= scale.c index b65a055d0a..b953e7c563 100644 --- a/tests/tcg/i386/test-i386-fscale.c +++ b/tests/tcg/i386/test-i386-fscale.c @@ -31,6 +31,7 @@ int issignaling_ld(long double x) =20 int main(void) { + short cw; int ret =3D 0; __asm__ volatile ("fscale" : "=3Dt" (ld_res) : "0" (2.5L), "u" (__builtin_nansl(""))); @@ -62,5 +63,33 @@ int main(void) printf("FAIL: fscale invalid 4\n"); ret =3D 1; } + __asm__ volatile ("fscale" : "=3Dt" (ld_res) : + "0" (0.0L), "u" (__builtin_infl())); + if (!isnan_ld(ld_res) || issignaling_ld(ld_res)) { + printf("FAIL: fscale 0 up inf\n"); + ret =3D 1; + } + __asm__ volatile ("fscale" : "=3Dt" (ld_res) : + "0" (__builtin_infl()), "u" (-__builtin_infl())); + if (!isnan_ld(ld_res) || issignaling_ld(ld_res)) { + printf("FAIL: fscale inf down inf\n"); + ret =3D 1; + } + /* Set round-downward. */ + __asm__ volatile ("fnstcw %0" : "=3Dm" (cw)); + cw =3D (cw & ~0xc00) | 0x400; + __asm__ volatile ("fldcw %0" : : "m" (cw)); + __asm__ volatile ("fscale" : "=3Dt" (ld_res) : + "0" (1.0L), "u" (__builtin_infl())); + if (ld_res !=3D __builtin_infl()) { + printf("FAIL: fscale finite up inf\n"); + ret =3D 1; + } + __asm__ volatile ("fscale" : "=3Dt" (ld_res) : + "0" (-1.0L), "u" (-__builtin_infl())); + if (ld_res !=3D -0.0L || __builtin_copysignl(1.0L, ld_res) !=3D -1.0L)= { + printf("FAIL: fscale finite down inf\n"); + ret =3D 1; + } return ret; } --=20 2.26.2