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| author | Richard Henderson <richard.henderson@linaro.org> | 2021-03-14 16:49:30 -0600 |
|---|---|---|
| committer | Richard Henderson <richard.henderson@linaro.org> | 2021-03-15 12:47:08 -0600 |
| commit | 7625a1ed013a042748753750c9d9b1a33c9cd8e0 (patch) | |
| tree | d55ac781e64eff379c8cb99dc4af24896850c3bc /util | |
| parent | 51204c2f188ec1e2a38f14718d38a3772f850a4b (diff) | |
| download | qemu-7625a1ed013a042748753750c9d9b1a33c9cd8e0.zip qemu-7625a1ed013a042748753750c9d9b1a33c9cd8e0.tar.gz qemu-7625a1ed013a042748753750c9d9b1a33c9cd8e0.tar.bz2 | |
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>
Message-Id: <20210315155835.1970210-2-richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Diffstat (limited to 'util')
| -rw-r--r-- | util/cutils.c | 50 |
1 files changed, 35 insertions, 15 deletions
diff --git a/util/cutils.c b/util/cutils.c index d89a40a..c442882 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: |