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8150617: nth_bit and friends are broken

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Reviewed-by: shade, tschatzl, vlivanov
This commit is contained in:
Stefan Karlsson 2016-02-25 13:08:19 +01:00
parent a8672f2267
commit d15936bdc0
2 changed files with 16 additions and 2 deletions
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14
hotspot/src/share/vm/utilities/globalDefinitions.cpp
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@ -358,6 +358,20 @@ size_t lcm(size_t a, size_t b) {
return size_t(result);
}
// Test that nth_bit macro and friends behave as
// expected, even with low-precedence operators.
STATIC_ASSERT(nth_bit(3) == 0x8);
STATIC_ASSERT(nth_bit(1|2) == 0x8);
STATIC_ASSERT(right_n_bits(3) == 0x7);
STATIC_ASSERT(right_n_bits(1|2) == 0x7);
STATIC_ASSERT(left_n_bits(3) == (intptr_t) LP64_ONLY(0xE000000000000000) NOT_LP64(0xE0000000));
STATIC_ASSERT(left_n_bits(1|2) == (intptr_t) LP64_ONLY(0xE000000000000000) NOT_LP64(0xE0000000));
#ifndef PRODUCT
// For unit testing only
class GlobalDefinitions {

4
hotspot/src/share/vm/utilities/globalDefinitions.hpp
View File

@ -1083,9 +1083,9 @@ const intptr_t OneBit = 1; // only right_most bit set in a word
// get a word with the n.th or the right-most or left-most n bits set
// (note: #define used only so that they can be used in enum constant definitions)
#define nth_bit(n) (n >= BitsPerWord ? 0 : OneBit << (n))
#define nth_bit(n) (((n) >= BitsPerWord) ? 0 : (OneBit << (n)))
#define right_n_bits(n) (nth_bit(n) - 1)
#define left_n_bits(n) (right_n_bits(n) << (n >= BitsPerWord ? 0 : (BitsPerWord - n)))
#define left_n_bits(n) (right_n_bits(n) << (((n) >= BitsPerWord) ? 0 : (BitsPerWord - (n))))
// bit-operations using a mask m
inline void set_bits (intptr_t& x, intptr_t m) { x |= m; }