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| author | Gabe Black <gblack@eecs.umich.edu> | 2009-07-01 22:16:36 -0700 |
|---|---|---|
| committer | Gabe Black <gblack@eecs.umich.edu> | 2009-07-01 22:16:36 -0700 |
| commit | 7172e26cc446556e6b8241549d5d188b5cb0cd37 (patch) | |
| tree | 38ac996fee85f4ed7a03c0e8e4f725a46821675e | |
| parent | f5141c23fd63c0fd89828ebf91317b1bd7f77881 (diff) | |
| download | gem5-7172e26cc446556e6b8241549d5d188b5cb0cd37.tar.xz | |
ARM: Add a findLsbSet function and use it to implement clz.
| -rw-r--r-- | src/arch/arm/isa/decoder.isa | 14 | ||||
| -rw-r--r-- | src/base/bitfield.hh | 17 |
2 files changed, 19 insertions, 12 deletions
diff --git a/src/arch/arm/isa/decoder.isa b/src/arch/arm/isa/decoder.isa index 9d2c90b4c..8c9f7aa50 100644 --- a/src/arch/arm/isa/decoder.isa +++ b/src/arch/arm/isa/decoder.isa @@ -270,18 +270,8 @@ format DataOp { 0x1: decode OPCODE { 0x9: BranchExchange::bx({{ }}); 0xb: PredOp::clz({{ - if (Rm == 0) - Rd = 32; - else - { - int i; - for (i = 0; i < 32; i++) - { - if (Rm & (1<<(31-i))) - break; - } - Rd = i; - } + unsigned lsb = findLsbSet(Rm); + Rd = (lsb > 31) ? 32 : lsb; }}); } 0x2: decode OPCODE { diff --git a/src/base/bitfield.hh b/src/base/bitfield.hh index 28093a5d4..cc3695159 100644 --- a/src/base/bitfield.hh +++ b/src/base/bitfield.hh @@ -161,4 +161,21 @@ findMsbSet(uint64_t val) { return msb; } +/** + * Returns the bit position of the LSB that is set in the input + */ +inline int +findLsbSet(uint64_t val) { + int lsb = 0; + if (!val) + return sizeof(val) * 8; + if (!bits(val, 31,0)) { lsb += 32; val >>= 32; } + if (!bits(val, 15,0)) { lsb += 16; val >>= 16; } + if (!bits(val, 7,0)) { lsb += 8; val >>= 8; } + if (!bits(val, 3,0)) { lsb += 4; val >>= 4; } + if (!bits(val, 1,0)) { lsb += 2; val >>= 2; } + if (!bits(val, 0,0)) { lsb += 1; } + return lsb; +} + #endif // __BASE_BITFIELD_HH__ |