[llvm] 1095419 - [llvm][StringExtras] Add a fail-able version of `fromHex`
River Riddle via llvm-commits
llvm-commits at lists.llvm.org
Wed Oct 28 17:03:55 PDT 2020
Author: River Riddle
Date: 2020-10-28T16:58:06-07:00
New Revision: 1095419b10ff222c3cc362be27d97ff561a2181b
URL: https://github.com/llvm/llvm-project/commit/1095419b10ff222c3cc362be27d97ff561a2181b
DIFF: https://github.com/llvm/llvm-project/commit/1095419b10ff222c3cc362be27d97ff561a2181b.diff
LOG: [llvm][StringExtras] Add a fail-able version of `fromHex`
This revision adds a fail-able/checked version of `fromHex` that fails when the input string contains a non-hex character. This removes the need for users to have a separate check for if the string contains all hex digits. This becomes very costly for large hex strings given that checking if a string contains only hex digits is effectively the same as just converting it in the first place.
Context: In MLIR we use hex strings to represent very large constants in the textual format of the IR. These changes lead to a large decrease in compile time when parsing these constants (2 seconds -> 1 second).
Differential Revision: https://reviews.llvm.org/D90265
Added:
Modified:
llvm/include/llvm/ADT/StringExtras.h
llvm/unittests/ADT/StringExtrasTest.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/ADT/StringExtras.h b/llvm/include/llvm/ADT/StringExtras.h
index 990a3054a9d2..6084a564b95d 100644
--- a/llvm/include/llvm/ADT/StringExtras.h
+++ b/llvm/include/llvm/ADT/StringExtras.h
@@ -165,34 +165,68 @@ inline std::string toHex(ArrayRef<uint8_t> Input, bool LowerCase = false) {
return toHex(toStringRef(Input), LowerCase);
}
-inline uint8_t hexFromNibbles(char MSB, char LSB) {
+/// Store the binary representation of the two provided values, \p MSB and
+/// \p LSB, that make up the nibbles of a hexadecimal digit. If \p MSB or \p LSB
+/// do not correspond to proper nibbles of a hexadecimal digit, this method
+/// returns false. Otherwise, returns true.
+inline bool tryGetHexFromNibbles(char MSB, char LSB, uint8_t &Hex) {
unsigned U1 = hexDigitValue(MSB);
unsigned U2 = hexDigitValue(LSB);
- assert(U1 != -1U && U2 != -1U);
+ if (U1 == -1U || U2 == -1U)
+ return false;
- return static_cast<uint8_t>((U1 << 4) | U2);
+ Hex = static_cast<uint8_t>((U1 << 4) | U2);
+ return true;
}
-/// Convert hexadecimal string \p Input to its binary representation.
-/// The return string is half the size of \p Input.
-inline std::string fromHex(StringRef Input) {
+/// Return the binary representation of the two provided values, \p MSB and
+/// \p LSB, that make up the nibbles of a hexadecimal digit.
+inline uint8_t hexFromNibbles(char MSB, char LSB) {
+ uint8_t Hex = 0;
+ bool GotHex = tryGetHexFromNibbles(MSB, LSB, Hex);
+ (void)GotHex;
+ assert(GotHex && "MSB and/or LSB do not correspond to hex digits");
+ return Hex;
+}
+
+/// Convert hexadecimal string \p Input to its binary representation and store
+/// the result in \p Output. Returns true if the binary representation could be
+/// converted from the hexadecimal string. Returns false if \p Input contains
+/// non-hexadecimal digits. The output string is half the size of \p Input.
+inline bool tryGetFromHex(StringRef Input, std::string &Output) {
if (Input.empty())
- return std::string();
+ return true;
- std::string Output;
Output.reserve((Input.size() + 1) / 2);
if (Input.size() % 2 == 1) {
- Output.push_back(hexFromNibbles('0', Input.front()));
+ uint8_t Hex = 0;
+ if (!tryGetHexFromNibbles('0', Input.front(), Hex))
+ return false;
+
+ Output.push_back(Hex);
Input = Input.drop_front();
}
assert(Input.size() % 2 == 0);
while (!Input.empty()) {
- uint8_t Hex = hexFromNibbles(Input[0], Input[1]);
+ uint8_t Hex = 0;
+ if (!tryGetHexFromNibbles(Input[0], Input[1], Hex))
+ return false;
+
Output.push_back(Hex);
Input = Input.drop_front(2);
}
- return Output;
+ return true;
+}
+
+/// Convert hexadecimal string \p Input to its binary representation.
+/// The return string is half the size of \p Input.
+inline std::string fromHex(StringRef Input) {
+ std::string Hex;
+ bool GotHex = tryGetFromHex(Input, Hex);
+ (void)GotHex;
+ assert(GotHex && "Input contains non hex digits");
+ return Hex;
}
/// Convert the string \p S to an integer of the specified type using
diff --git a/llvm/unittests/ADT/StringExtrasTest.cpp b/llvm/unittests/ADT/StringExtrasTest.cpp
index d17a172dbd9c..b785bb51844b 100644
--- a/llvm/unittests/ADT/StringExtrasTest.cpp
+++ b/llvm/unittests/ADT/StringExtrasTest.cpp
@@ -89,6 +89,10 @@ TEST(StringExtrasTest, ToAndFromHex) {
EXPECT_EQ(EvenStr, toHex(EvenData));
EXPECT_EQ(EvenData, fromHex(EvenStr));
EXPECT_EQ(StringRef(EvenStr).lower(), toHex(EvenData, true));
+
+ std::string InvalidStr = "A5ZX";
+ std::string IgnoredOutput;
+ EXPECT_FALSE(tryGetFromHex(InvalidStr, IgnoredOutput));
}
TEST(StringExtrasTest, to_float) {
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