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[Support] Add type generic bit utilities to MathExtras.h

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182667 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Michael J. Spencer 2013-05-24 20:29:47 +00:00
parent 959ecb2eec
commit 36fe3f2b56
2 changed files with 303 additions and 0 deletions
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212
include/llvm/Support/MathExtras.h
View File

@ -15,12 +15,224 @@
#define LLVM_SUPPORT_MATHEXTRAS_H
#include "llvm/Support/SwapByteOrder.h"
#include "llvm/Support/type_traits.h"
#include <cstring>
#ifdef _MSC_VER
# include <intrin.h>
#endif
namespace llvm {
/// \brief The behavior an operation has on an input of 0.
enum ZeroBehavior {
/// \brief The returned value is undefined.
ZB_Undefined,
/// \brief The returned value is numeric_limits<T>::max()
ZB_Max,
/// \brief The returned value is numeric_limits<T>::digits
ZB_Width
};
/// \brief Count number of 0's from the least significant bit to the most
/// stopping at the first 1.
///
/// Only unsigned integral types are allowed.
///
/// \param ZB the behavior on an input of 0. Only ZB_Width and ZB_Undefined are
/// valid arguments.
template <typename T>
typename enable_if_c<std::numeric_limits<T>::is_integer &&
!std::numeric_limits<T>::is_signed, std::size_t>::type
countTrailingZeros(T Val, ZeroBehavior ZB = ZB_Width) {
if (!Val)
return std::numeric_limits<T>::digits;
if (Val & 0x1)
return 0;
// Bisection method.
std::size_t ZeroBits = 0;
T Shift = std::numeric_limits<T>::digits >> 1;
T Mask = std::numeric_limits<T>::max() >> Shift;
while (Shift) {
if ((Val & Mask) == 0) {
Val >>= Shift;
ZeroBits |= Shift;
}
Shift >>= 1;
Mask >>= Shift;
}
return ZeroBits;
}
// Disable signed.
template <typename T>
typename enable_if_c<std::numeric_limits<T>::is_integer &&
std::numeric_limits<T>::is_signed, std::size_t>::type
countTrailingZeros(T Val, ZeroBehavior ZB = ZB_Width) LLVM_DELETED_FUNCTION;
#if __GNUC__ >= 4 || _MSC_VER
template <>
inline std::size_t countTrailingZeros<uint32_t>(uint32_t Val, ZeroBehavior ZB) {
if (ZB != ZB_Undefined && Val == 0)
return 32;
#if __GNUC__ >= 4
return __builtin_ctz(Val);
#elif _MSC_VER
unsigned long Index;
_BitScanForward(&Index, Val);
return Index;
#endif
}
template <>
inline std::size_t countTrailingZeros<uint64_t>(uint64_t Val, ZeroBehavior ZB) {
if (ZB != ZB_Undefined && Val == 0)
return 64;
#if __GNUC__ >= 4
return __builtin_ctzll(Val);
#elif _MSC_VER
unsigned long Index;
_BitScanForward64(&Index, Val);
return Index;
#endif
}
#endif
/// \brief Count number of 0's from the most significant bit to the least
/// stopping at the first 1.
///
/// Only unsigned integral types are allowed.
///
/// \param ZB the behavior on an input of 0. Only ZB_Width and ZB_Undefined are
/// valid arguments.
template <typename T>
typename enable_if_c<std::numeric_limits<T>::is_integer &&
!std::numeric_limits<T>::is_signed, std::size_t>::type
countLeadingZeros(T Val, ZeroBehavior ZB = ZB_Width) {
if (!Val)
return std::numeric_limits<T>::digits;
// Bisection method.
std::size_t ZeroBits = 0;
for (T Shift = std::numeric_limits<T>::digits >> 1; Shift; Shift >>= 1) {
T Tmp = Val >> Shift;
if (Tmp)
Val = Tmp;
else
ZeroBits |= Shift;
}
return ZeroBits;
}
// Disable signed.
template <typename T>
typename enable_if_c<std::numeric_limits<T>::is_integer &&
std::numeric_limits<T>::is_signed, std::size_t>::type
countLeadingZeros(T Val, ZeroBehavior ZB = ZB_Width) LLVM_DELETED_FUNCTION;
#if __GNUC__ >= 4 || _MSC_VER
template <>
inline std::size_t countLeadingZeros<uint32_t>(uint32_t Val, ZeroBehavior ZB) {
if (ZB != ZB_Undefined && Val == 0)
return 32;
#if __GNUC__ >= 4
return __builtin_clz(Val);
#elif _MSC_VER
unsigned long Index;
_BitScanReverse(&Index, Val);
return Index ^ 31;
#endif
}
template <>
inline std::size_t countLeadingZeros<uint64_t>(uint64_t Val, ZeroBehavior ZB) {
if (ZB != ZB_Undefined && Val == 0)
return 64;
#if __GNUC__ >= 4
return __builtin_clzll(Val);
#elif _MSC_VER
unsigned long Index;
_BitScanReverse64(&Index, Val);
return Index ^ 63;
#endif
}
#endif
/// \brief Get the index of the first set bit starting from the least
/// significant bit.
///
/// Only unsigned integral types are allowed.
///
/// \param ZB the behavior on an input of 0. Only ZB_Max and ZB_Undefined are
/// valid arguments.
template <typename T>
typename enable_if_c<std::numeric_limits<T>::is_integer &&
!std::numeric_limits<T>::is_signed, std::size_t>::type
findFirstSet(T Val, ZeroBehavior ZB = ZB_Max) {
if (ZB == ZB_Max && Val == 0)
return std::numeric_limits<T>::max();
return countTrailingZeros(Val, ZB_Undefined);
}
// Disable signed.
template <typename T>
typename enable_if_c<std::numeric_limits<T>::is_integer &&
std::numeric_limits<T>::is_signed, std::size_t>::type
findFirstSet(T Val, ZeroBehavior ZB = ZB_Max) LLVM_DELETED_FUNCTION;
/// \brief Get the index of the last set bit starting from the least
/// significant bit.
///
/// Only unsigned integral types are allowed.
///
/// \param ZB the behavior on an input of 0. Only ZB_Max and ZB_Undefined are
/// valid arguments.
template <typename T>
typename enable_if_c<std::numeric_limits<T>::is_integer &&
!std::numeric_limits<T>::is_signed, std::size_t>::type
findLastSet(T Val, ZeroBehavior ZB = ZB_Max) {
if (ZB == ZB_Max && Val == 0)
return std::numeric_limits<T>::max();
// Use ^ instead of - because both gcc and llvm can remove the associated ^
// in the __builtin_clz intrinsic on x86.
return countLeadingZeros(Val, ZB_Undefined) ^
(std::numeric_limits<T>::digits - 1);
}
// Disable signed.
template <typename T>
typename enable_if_c<std::numeric_limits<T>::is_integer &&
std::numeric_limits<T>::is_signed, std::size_t>::type
findLastSet(T Val, ZeroBehavior ZB = ZB_Max) LLVM_DELETED_FUNCTION;
/// \brief Macro compressed bit reversal table for 256 bits.
///
/// http://graphics.stanford.edu/~seander/bithacks.html#BitReverseTable
static const unsigned char BitReverseTable256[256] = {
#define R2(n) n, n + 2 * 64, n + 1 * 64, n + 3 * 64
#define R4(n) R2(n), R2(n + 2 * 16), R2(n + 1 * 16), R2(n + 3 * 16)
#define R6(n) R4(n), R4(n + 2 * 4), R4(n + 1 * 4), R4(n + 3 * 4)
R6(0), R6(2), R6(1), R6(3)
};
/// \brief Reverse the bits in \p Val.
template <typename T>
T reverseBits(T Val) {
unsigned char in[sizeof(Val)];
unsigned char out[sizeof(Val)];
std::memcpy(in, &Val, sizeof(Val));
for (unsigned i = 0; i < sizeof(Val); ++i)
out[(sizeof(Val) - i) - 1] = BitReverseTable256[in[i]];
std::memcpy(&Val, out, sizeof(Val));
return Val;
}
// NOTE: The following support functions use the _32/_64 extensions instead of
// type overloading so that signed and unsigned integers can be used without

91
unittests/Support/MathExtrasTest.cpp
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@ -14,6 +14,97 @@ using namespace llvm;
namespace {
TEST(MathExtras, countTrailingZeros) {
uint8_t Z8 = 0;
uint16_t Z16 = 0;
uint32_t Z32 = 0;
uint64_t Z64 = 0;
EXPECT_EQ(8, countTrailingZeros(Z8));
EXPECT_EQ(16, countTrailingZeros(Z16));
EXPECT_EQ(32, countTrailingZeros(Z32));
EXPECT_EQ(64, countTrailingZeros(Z64));
uint8_t NZ8 = 42;
uint16_t NZ16 = 42;
uint32_t NZ32 = 42;
uint64_t NZ64 = 42;
EXPECT_EQ(1, countTrailingZeros(NZ8));
EXPECT_EQ(1, countTrailingZeros(NZ16));
EXPECT_EQ(1, countTrailingZeros(NZ32));
EXPECT_EQ(1, countTrailingZeros(NZ64));
}
TEST(MathExtras, countLeadingZeros) {
uint8_t Z8 = 0;
uint16_t Z16 = 0;
uint32_t Z32 = 0;
uint64_t Z64 = 0;
EXPECT_EQ(8, countLeadingZeros(Z8));
EXPECT_EQ(16, countLeadingZeros(Z16));
EXPECT_EQ(32, countLeadingZeros(Z32));
EXPECT_EQ(64, countLeadingZeros(Z64));
uint8_t NZ8 = 42;
uint16_t NZ16 = 42;
uint32_t NZ32 = 42;
uint64_t NZ64 = 42;
EXPECT_EQ(2, countLeadingZeros(NZ8));
EXPECT_EQ(10, countLeadingZeros(NZ16));
EXPECT_EQ(26, countLeadingZeros(NZ32));
EXPECT_EQ(58, countLeadingZeros(NZ64));
}
TEST(MathExtras, findFirstSet) {
uint8_t Z8 = 0;
uint16_t Z16 = 0;
uint32_t Z32 = 0;
uint64_t Z64 = 0;
EXPECT_EQ(0xFF, findFirstSet(Z8));
EXPECT_EQ(0xFFFF, findFirstSet(Z16));
EXPECT_EQ(0xFFFFFFFF, findFirstSet(Z32));
EXPECT_EQ(0xFFFFFFFFFFFFFFFF, findFirstSet(Z64));
uint8_t NZ8 = 42;
uint16_t NZ16 = 42;
uint32_t NZ32 = 42;
uint64_t NZ64 = 42;
EXPECT_EQ(1, findFirstSet(NZ8));
EXPECT_EQ(1, findFirstSet(NZ16));
EXPECT_EQ(1, findFirstSet(NZ32));
EXPECT_EQ(1, findFirstSet(NZ64));
}
TEST(MathExtras, findLastSet) {
uint8_t Z8 = 0;
uint16_t Z16 = 0;
uint32_t Z32 = 0;
uint64_t Z64 = 0;
EXPECT_EQ(0xFF, findLastSet(Z8));
EXPECT_EQ(0xFFFF, findLastSet(Z16));
EXPECT_EQ(0xFFFFFFFF, findLastSet(Z32));
EXPECT_EQ(0xFFFFFFFFFFFFFFFF, findLastSet(Z64));
uint8_t NZ8 = 42;
uint16_t NZ16 = 42;
uint32_t NZ32 = 42;
uint64_t NZ64 = 42;
EXPECT_EQ(5, findLastSet(NZ8));
EXPECT_EQ(5, findLastSet(NZ16));
EXPECT_EQ(5, findLastSet(NZ32));
EXPECT_EQ(5, findLastSet(NZ64));
}
TEST(MathExtras, reverseBits) {
uint8_t NZ8 = 42;
uint16_t NZ16 = 42;
uint32_t NZ32 = 42;
uint64_t NZ64 = 42;
EXPECT_EQ(0x54, reverseBits(NZ8));
EXPECT_EQ(0x5400, reverseBits(NZ16));
EXPECT_EQ(0x54000000, reverseBits(NZ32));
EXPECT_EQ(0x5400000000000000, reverseBits(NZ64));
}
TEST(MathExtras, isPowerOf2_32) {
EXPECT_TRUE(isPowerOf2_32(1 << 6));
EXPECT_TRUE(isPowerOf2_32(1 << 12));