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[187.189.51.144]) by smtp.gmail.com with ESMTPSA id h24sm7278548otg.20.2021.03.15.08.58.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Mar 2021 08:58:40 -0700 (PDT) From: Richard Henderson To: qemu-devel@nongnu.org Subject: [PATCH v2 1/1] utils: Use fixed-point arithmetic in qemu_strtosz Date: Mon, 15 Mar 2021 09:58:35 -0600 Message-Id: <20210315155835.1970210-2-richard.henderson@linaro.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210315155835.1970210-1-richard.henderson@linaro.org> References: <20210315155835.1970210-1-richard.henderson@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2607:f8b0:4864:20::336; envelope-from=richard.henderson@linaro.org; helo=mail-ot1-x336.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no 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: philmd@redhat.com, thuth@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Once we've parsed the fractional value, extract it into an integral 64-bit fraction. Perform the scaling with integer arithemetic, and simplify the overflow detection. Signed-off-by: Richard Henderson Reviewed-by: Eric Blake --- tests/unit/test-cutils.c | 2 +- util/cutils.c | 50 ++++++++++++++++++++++++++++------------ 2 files changed, 36 insertions(+), 16 deletions(-) diff --git a/tests/unit/test-cutils.c b/tests/unit/test-cutils.c index bad3a60993..e025b54c05 100644 --- a/tests/unit/test-cutils.c +++ b/tests/unit/test-cutils.c @@ -2128,7 +2128,7 @@ static void test_qemu_strtosz_float(void) str = "12.345M"; err = qemu_strtosz(str, &endptr, &res); g_assert_cmpint(err, ==, 0); - g_assert_cmpint(res, ==, (uint64_t) (12.345 * MiB)); + g_assert_cmpint(res, ==, (uint64_t) (12.345 * MiB + 0.5)); g_assert(endptr == str + 7); } diff --git a/util/cutils.c b/util/cutils.c index d89a40a8c3..c442882b88 100644 --- a/util/cutils.c +++ b/util/cutils.c @@ -275,10 +275,9 @@ static int do_strtosz(const char *nptr, const char **end, int retval; const char *endptr, *f; unsigned char c; - bool mul_required = false, hex = false; - uint64_t val; + bool hex = false; + uint64_t val, valf = 0; int64_t mul; - double fraction = 0.0; /* Parse integral portion as decimal. */ retval = qemu_strtou64(nptr, &endptr, 10, &val); @@ -308,17 +307,19 @@ static int do_strtosz(const char *nptr, const char **end, * without fractional digits. If we see an exponent, treat * the entire input as invalid instead. */ + double fraction; + f = endptr; retval = qemu_strtod_finite(f, &endptr, &fraction); if (retval) { - fraction = 0.0; endptr++; } else if (memchr(f, 'e', endptr - f) || memchr(f, 'E', endptr - f)) { endptr = nptr; retval = -EINVAL; goto out; - } else if (fraction != 0) { - mul_required = true; + } else { + /* Extract into a 64-bit fixed-point fraction. */ + valf = (uint64_t)(fraction * 0x1p64); } } c = *endptr; @@ -333,16 +334,35 @@ static int do_strtosz(const char *nptr, const char **end, mul = suffix_mul(default_suffix, unit); assert(mul > 0); } - if (mul == 1 && mul_required) { - endptr = nptr; - retval = -EINVAL; - goto out; + if (mul == 1) { + /* When a fraction is present, a scale is required. */ + if (valf != 0) { + endptr = nptr; + retval = -EINVAL; + goto out; + } + } else { + uint64_t valh, tmp; + + /* Compute exact result: 64.64 x 64.0 -> 128.64 fixed point */ + mulu64(&val, &valh, val, mul); + mulu64(&valf, &tmp, valf, mul); + val += tmp; + valh += val < tmp; + + /* Round 0.5 upward. */ + tmp = valf >> 63; + val += tmp; + valh += val < tmp; + + /* Report overflow. */ + if (valh != 0) { + retval = -ERANGE; + goto out; + } } - if (val > (UINT64_MAX - ((uint64_t) (fraction * mul))) / mul) { - retval = -ERANGE; - goto out; - } - *result = val * mul + (uint64_t) (fraction * mul); + + *result = val; retval = 0; out: