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| author | Richard Henderson | 2021-03-15 19:51:17 +0100 |
|---|---|---|
| committer | Alex Bennée | 2021-03-17 08:16:59 +0100 |
| commit | 6567ba0c60d6e1366f7ac6e77665730e657e8eca (patch) | |
| tree | 92abe05dedd247630a82e526bd28098873929736 | |
| parent | Merge remote-tracking branch 'remotes/kraxel/tags/usb-20210315-pull-request' ... (diff) | |
| download | qemu-6567ba0c60d6e1366f7ac6e77665730e657e8eca.tar.gz qemu-6567ba0c60d6e1366f7ac6e77665730e657e8eca.tar.xz qemu-6567ba0c60d6e1366f7ac6e77665730e657e8eca.zip | |
utils: Use fixed-point arithmetic in qemu_strtosz
Once we've parsed the fractional value, extract it into an integral
64-bit fraction. Perform the scaling with integer arithmetic, and
simplify the overflow detection.
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210315185117.1986240-2-richard.henderson@linaro.org>
| -rw-r--r-- | tests/unit/test-cutils.c | 2 | ||||
| -rw-r--r-- | 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 (val > (UINT64_MAX - ((uint64_t) (fraction * mul))) / mul) { - retval = -ERANGE; - 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; + } } - *result = val * mul + (uint64_t) (fraction * mul); + + *result = val; retval = 0; out: |