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fmt: fuzz, remove some unnecessary busywork

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Removing some signed checks and logic where we've already guaranteed the
values to be positive.  Indeed, in these cases, if a negative value got
through (per my realisation in the signed fuzz harness), it would cause
an infinite loop due to flooring division.
This commit is contained in:
Charlotte 2023-06-28 11:51:24 +10:00 • committed by Marcelina Kościelnicka
parent 2ae551c0af
commit 3571bf2c2d
4 changed files with 55 additions and 20 deletions
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5
backends/cxxrtl/cxxrtl.h
View file

@ -905,10 +905,7 @@ std::ostream &operator<<(std::ostream &os, const value_formatted<Bits> &vf)
buf += '0';
while (!val.is_zero()) {
value<Bits> quotient;
if (negative)
val.signedDivideWithRemainder(value<Bits>{10u}, quotient);
else
val.divideWithRemainder(value<Bits>{10u}, quotient);
val.divideWithRemainder(value<Bits>{10u}, quotient);
buf += '0' + val.template slice<3, 0>().val().template get<uint8_t>();
val = quotient;
}

4
kernel/fmt.cc
View file

@ -680,8 +680,8 @@ std::string Fmt::render() const
if (absvalue.is_fully_zero())
buf += '0';
while (!absvalue.is_fully_zero()) {
buf += '0' + RTLIL::const_mod(absvalue, 10, part.signed_, false, 4).as_int();
absvalue = RTLIL::const_div(absvalue, 10, part.signed_, false, absvalue.size());
buf += '0' + RTLIL::const_mod(absvalue, 10, false, false, 4).as_int();
absvalue = RTLIL::const_div(absvalue, 10, false, false, absvalue.size());
}
if (negative || part.plus)
buf += negative ? '-' : '+';

1
tests/fmt/fuzz/CMakeLists.txt
View file

@ -17,6 +17,7 @@ add_executable(
x_test
x_test.cc
../../../libs/bigint/BigUnsigned.cc
../../../libs/bigint/BigInteger.cc
)
link_fuzztest(x_test)

65
tests/fmt/fuzz/x_test.cc
View file

@ -4,34 +4,33 @@
#include <sstream>
#include "backends/cxxrtl/cxxrtl.h"
#include "libs/bigint/BigUnsigned.hh"
#include "libs/bigint/BigInteger.hh"
using namespace cxxrtl_yosys;
void Formats128BitUnsignedIntegers(uint64_t x, uint64_t y) {
// Compare output to actual BigUnsigned.
value<64> vs;
void Formats128BitUnsignedIntegers(chunk_t x0, chunk_t x1, chunk_t x2, chunk_t x3)
{
// Compare output to BigUnsigned.
value<128> v;
vs.set(x);
v = v.blit<127, 64>(vs);
vs.set(y);
v = v.blit<63, 0>(vs);
v = v.blit<127, 64>(value<64>{x1, x0});
v = v.blit<63, 0>(value<64>{x3, x2});
std::ostringstream oss;
oss << value_formatted<128>(v, false, false, ' ', 0, 10, false, false, false);
auto actual = oss.str();
BigUnsigned b(x);
b.bitShiftLeft(b, 64);
b.bitOr(b, y);
BigUnsigned u;
u.bitShiftLeft(v.slice<127, 64>().val().get<uint64_t>(), 64);
u.bitOr(u, v.slice<63, 0>().val().get<uint64_t>());
std::string expected;
if (b.isZero()) {
if (u.isZero()) {
expected = "0";
} else {
while (!b.isZero()) {
expected += '0' + (b % 10).toInt();
b /= 10;
while (!u.isZero()) {
expected += '0' + (u % 10).toInt();
u /= 10;
}
std::reverse(expected.begin(), expected.end());
}
@ -40,3 +39,41 @@ void Formats128BitUnsignedIntegers(uint64_t x, uint64_t y) {
}
FUZZ_TEST(CxxrtlDivisionFuzz, Formats128BitUnsignedIntegers);
void Formats128BitSignedIntegers(chunk_t x0, chunk_t x1, chunk_t x2, chunk_t x3) {
// Compare output to BigInteger.
value<128> v;
v = v.blit<127, 64>(value<64>{x1, x0});
v = v.blit<63, 0>(value<64>{x3, x2});
std::ostringstream oss;
oss << value_formatted<128>(v, false, false, ' ', 0, 10, true, false, false);
auto actual = oss.str();
BigUnsigned u;
bool negative = v.is_neg();
if (negative)
v = v.neg();
u.bitShiftLeft(v.slice<127, 64>().val().get<uint64_t>(), 64);
u.bitOr(u, v.slice<63, 0>().val().get<uint64_t>());
std::string expected;
if (u.isZero()) {
expected = "0";
} else {
// Note that we never actually do division of negative numbers: our division
// routines are flooring, not truncating, so dividing by 10 repeatedly won't
// necessarily ever get to zero.
while (!u.isZero()) {
expected += '0' + (u % 10).toInt();
u /= 10;
}
if (negative) {
expected += '-';
}
std::reverse(expected.begin(), expected.end());
}
EXPECT_EQ(actual, expected);
}
FUZZ_TEST(CxxrtlDivisionFuzz, Formats128BitSignedIntegers);