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ARM: Add a findLsbSet function and use it to implement clz.

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This commit is contained in:
Gabe Black 2009-07-01 22:16:36 -07:00
parent f5141c23fd
commit 7172e26cc4
2 changed files with 19 additions and 12 deletions
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14
src/arch/arm/isa/decoder.isa
View file

@ -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 {

17
src/base/bitfield.hh
View file

@ -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__