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Add specialization for small numbers.

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This commit is contained in:
chriseth 2020-09-15 14:25:07 +02:00
parent 858b4507e2
commit 55e6a92692
1 changed files with 31 additions and 0 deletions
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31
libsolidity/codegen/YulUtilFunctions.cpp
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@ -632,6 +632,16 @@ string YulUtilFunctions::overflowCheckedIntExpFunction(
string YulUtilFunctions::overflowCheckedUnsignedExpFunction()
{
// Checks for the "small number specialization" below.
using namespace boost::multiprecision;
solAssert(pow(bigint(10), 77) < pow(bigint(2), 256), "");
solAssert(pow(bigint(11), 77) >= pow(bigint(2), 256), "");
solAssert(pow(bigint(10), 78) >= pow(bigint(2), 256), "");
solAssert(pow(bigint(306), 31) < pow(bigint(2), 256), "");
solAssert(pow(bigint(307), 31) >= pow(bigint(2), 256), "");
solAssert(pow(bigint(306), 32) >= pow(bigint(2), 256), "");
string functionName = "checked_exp_unsigned";
return m_functionCollector.createFunction(functionName, [&]() {
return
@ -644,6 +654,27 @@ string YulUtilFunctions::overflowCheckedUnsignedExpFunction()
if iszero(exponent) { power := 1 leave }
if iszero(base) { power := 0 leave }
// Specializations for small bases
switch base
// 0 is handled above
case 1 { power := 1 leave }
case 2
{
if gt(exponent, 255) { revert(0, 0) }
power := exp(2, exponent)
if gt(power, max) { revert(0, 0) }
leave
}
if or(
and(lt(base, 11), lt(exponent, 78)),
and(lt(base, 307), lt(exponent, 32))
)
{
power := exp(base, exponent)
if gt(power, max) { revert(0, 0) }
leave
}
power := 1
for { } gt(exponent, 1) {}