diff options
| -rw-r--r-- | src/compiler/nir/nir_opt_algebraic.py | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py index 2749b06aa69..8f08e6b1341 100644 --- a/src/compiler/nir/nir_opt_algebraic.py +++ b/src/compiler/nir/nir_opt_algebraic.py @@ -371,6 +371,37 @@ optimizations = [ 'options->lower_unpack_snorm_4x8'), ] +def fexp2i(exp): + # We assume that exp is already in the range [-126, 127]. + return ('ishl', ('iadd', exp, 127), 23) + +def ldexp32(f, exp): + # First, we clamp exp to a reasonable range. The maximum possible range + # for a normal exponent is [-126, 127] and, throwing in denormals, you get + # a maximum range of [-149, 127]. This means that we can potentially have + # a swing of +-276. If you start with FLT_MAX, you actually have to do + # ldexp(FLT_MAX, -278) to get it to flush all the way to zero. The GLSL + # spec, on the other hand, only requires that we handle an exponent value + # in the range [-126, 128]. This implementation is *mostly* correct; it + # handles a range on exp of [-252, 254] which allows you to create any + # value (including denorms if the hardware supports it) and to adjust the + # exponent of any normal value to anything you want. + exp = ('imin', ('imax', exp, -252), 254) + + # Now we compute two powers of 2, one for exp/2 and one for exp-exp/2. + # (We use ishr which isn't the same for -1, but the -1 case still works + # since we use exp-exp/2 as the second exponent.) While the spec + # technically defines ldexp as f * 2.0^exp, simply multiplying once doesn't + # work with denormals and doesn't allow for the full swing in exponents + # that you can get with normalized values. Instead, we create two powers + # of two and multiply by them each in turn. That way the effective range + # of our exponent is doubled. + pow2_1 = fexp2i(('ishr', exp, 1)) + pow2_2 = fexp2i(('isub', exp, ('ishr', exp, 1))) + return ('fmul', ('fmul', f, pow2_1), pow2_2) + +optimizations += [(('ldexp', 'x', 'exp'), ldexp32('x', 'exp'))] + # Unreal Engine 4 demo applications open-codes bitfieldReverse() def bitfield_reverse(u): step1 = ('ior', ('ishl', u, 16), ('ushr', u, 16)) |