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[Support] add decodeSLEB128()

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We already have routines to encode SLEB128 as well as encode/decode ULEB128.
This last function fills out the matrix.  I'll need this for some llvm-objdump
work I am doing.

llvm-svn: 217830
This commit is contained in:
Nick Kledzik 2014-09-15 21:51:49 +00:00
parent 48cecd5f82
commit 69a6312465
2 changed files with 56 additions and 0 deletions
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20
include/llvm/Support/LEB128.h
View File

@ -90,6 +90,26 @@ inline uint64_t decodeULEB128(const uint8_t *p, unsigned *n = nullptr) {
return Value;
}
/// Utility function to decode a SLEB128 value.
inline int64_t decodeSLEB128(const uint8_t *p, unsigned *n = nullptr) {
const uint8_t *orig_p = p;
int64_t Value = 0;
unsigned Shift = 0;
uint8_t Byte;
do {
Byte = *p++;
Value |= ((Byte & 0x7f) << Shift);
Shift += 7;
} while (Byte >= 128);
// Sign extend negative numbers.
if (Byte & 0x40)
Value |= (-1LL) << Shift;
if (n)
*n = (unsigned)(p - orig_p);
return Value;
}
/// Utility function to get the size of the ULEB128-encoded value.
extern unsigned getULEB128Size(uint64_t Value);

36
unittests/Support/LEB128Test.cpp
View File

@ -119,6 +119,42 @@ TEST(LEB128Test, DecodeULEB128) {
#undef EXPECT_DECODE_ULEB128_EQ
}
TEST(LEB128Test, DecodeSLEB128) {
#define EXPECT_DECODE_SLEB128_EQ(EXPECTED, VALUE) \
do { \
unsigned ActualSize = 0; \
int64_t Actual = decodeSLEB128(reinterpret_cast<const uint8_t *>(VALUE), \
&ActualSize); \
EXPECT_EQ(sizeof(VALUE) - 1, ActualSize); \
EXPECT_EQ(EXPECTED, Actual); \
} while (0)
// Decode SLEB128
EXPECT_DECODE_SLEB128_EQ(0L, "\x00");
EXPECT_DECODE_SLEB128_EQ(1L, "\x01");
EXPECT_DECODE_SLEB128_EQ(63L, "\x3f");
EXPECT_DECODE_SLEB128_EQ(-64L, "\x40");
EXPECT_DECODE_SLEB128_EQ(-63L, "\x41");
EXPECT_DECODE_SLEB128_EQ(-1L, "\x7f");
EXPECT_DECODE_SLEB128_EQ(128L, "\x80\x01");
EXPECT_DECODE_SLEB128_EQ(129L, "\x81\x01");
EXPECT_DECODE_SLEB128_EQ(-129L, "\xff\x7e");
EXPECT_DECODE_SLEB128_EQ(-128L, "\x80\x7f");
EXPECT_DECODE_SLEB128_EQ(-127L, "\x81\x7f");
EXPECT_DECODE_SLEB128_EQ(64L, "\xc0\x00");
EXPECT_DECODE_SLEB128_EQ(-12345L, "\xc7\x9f\x7f");
// Decode unnormalized SLEB128 with extra padding bytes.
EXPECT_DECODE_SLEB128_EQ(0L, "\x80\x00");
EXPECT_DECODE_SLEB128_EQ(0L, "\x80\x80\x00");
EXPECT_DECODE_SLEB128_EQ(0x7fL, "\xff\x00");
EXPECT_DECODE_SLEB128_EQ(0x7fL, "\xff\x80\x00");
EXPECT_DECODE_SLEB128_EQ(0x80L, "\x80\x81\x00");
EXPECT_DECODE_SLEB128_EQ(0x80L, "\x80\x81\x80\x00");
#undef EXPECT_DECODE_SLEB128_EQ
}
TEST(LEB128Test, SLEB128Size) {
// Positive Value Testing Plan:
// (1) 128 ^ n - 1 ........ need (n+1) bytes