---
src/compiler/nir/nir_opt_algebraic.py | 70 +++++++++++++++++++++++++++
1 file changed, 70 insertions(+)
diff --git a/src/compiler/nir/nir_opt_algebraic.py
b/src/compiler/nir/nir_opt_algebraic.py
index 3800db1da20..3384c9c2e67 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -890,10 +890,80 @@ def ldexp(f, exp, bits):
pow2_2 = fexp2i(('isub', exp, ('ishr', exp, 1)), bits)
return ('fmul', ('fmul', f, pow2_1), pow2_2)
+def ldexp_rtne(f, exp, bits):
+ # 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.
+ if bits == 16:
+ exp = ('imin', ('imax', exp, -28), 30)
+ elif bits == 32:
+ exp = ('imin', ('imax', exp, -252), 254)
+ elif bits == 64:
+ exp = ('imin', ('imax', exp, -2044), 2046)
+ else:
+ assert False
+
+ # 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), bits)
+ pow2_2 = fexp2i(('isub', exp, ('ishr', exp, 1)), bits)
+ return ('fmul_rtne', ('fmul_rtne', f, pow2_1), pow2_2)
+
+def ldexp_rtz(f, exp, bits):
+ # 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.
+ if bits == 16:
+ exp = ('imin', ('imax', exp, -28), 30)
+ elif bits == 32:
+ exp = ('imin', ('imax', exp, -252), 254)
+ elif bits == 64:
+ exp = ('imin', ('imax', exp, -2044), 2046)
+ else:
+ assert False
+
+ # 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), bits)
+ pow2_2 = fexp2i(('isub', exp, ('ishr', exp, 1)), bits)
+ return ('fmul_rtz', ('fmul_rtz', f, pow2_1), pow2_2)
+
optimizations += [
(('ldexp@16', 'x', 'exp'), ldexp('x', 'exp', 16), 'options->lower_ldexp'),
(('ldexp@32', 'x', 'exp'), ldexp('x', 'exp', 32), 'options->lower_ldexp'),
(('ldexp@64', 'x', 'exp'), ldexp('x', 'exp', 64), 'options->lower_ldexp'),
+ (('ldexp_rtne@16', 'x', 'exp'), ldexp_rtne('x', 'exp', 16),
'options->lower_ldexp'),
+ (('ldexp_rtne@32', 'x', 'exp'), ldexp_rtne('x', 'exp', 32),
'options->lower_ldexp'),
+ (('ldexp_rtne@64', 'x', 'exp'), ldexp_rtne('x', 'exp', 64),
'options->lower_ldexp'),
+ (('ldexp_rtz@16', 'x', 'exp'), ldexp_rtz('x', 'exp', 16),
'options->lower_ldexp'),
+ (('ldexp_rtz@32', 'x', 'exp'), ldexp_rtz('x', 'exp', 32),
'options->lower_ldexp'),
+ (('ldexp_rtz@64', 'x', 'exp'), ldexp_rtz('x', 'exp', 64),
'options->lower_ldexp'),
]
# Unreal Engine 4 demo applications open-codes bitfieldReverse()
--
2.19.1
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