Module: Mesa
Branch: vulkan
Commit: 08fe89864b94f970ce73368636a87eace3c81663
URL:
http://cgit.freedesktop.org/mesa/mesa/commit/?id=08fe89864b94f970ce73368636a87eace3c81663
Author: Jason Ekstrand <jason.ekstr...@intel.com>
Date: Fri Mar 25 12:09:33 2016 -0700
nir/algebraic: Add better lowering of ldexp
---
src/compiler/nir/nir_opt_algebraic.py | 29 +++++++++++++++++++++++++++--
1 file changed, 27 insertions(+), 2 deletions(-)
diff --git a/src/compiler/nir/nir_opt_algebraic.py
b/src/compiler/nir/nir_opt_algebraic.py
index ed21c5d..60cd731 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -276,8 +276,6 @@ optimizations = [
(('frem', a, b), ('fsub', a, ('fmul', b, ('ftrunc', ('fdiv', a, b)))),
'options->lower_fmod'),
(('uadd_carry', a, b), ('b2i', ('ult', ('iadd', a, b), a)),
'options->lower_uadd_carry'),
(('usub_borrow', a, b), ('b2i', ('ult', a, b)),
'options->lower_usub_borrow'),
- (('ldexp', 'x', 'exp'),
- ('fmul', 'x', ('ishl', ('imin', ('imax', ('iadd', 'exp', 0x7f), 0), 0xff),
23))),
(('bitfield_insert', 'base', 'insert', 'offset', 'bits'),
('bcsel', ('ilt', 31, 'bits'), 'insert',
@@ -359,6 +357,33 @@ optimizations = [
'options->lower_unpack_snorm_4x8'),
]
+def fexp2i(exp):
+ # We assume that exp is already in range.
+ return ('ishl', ('iadd', exp, 127), 23)
+
+def ldexp32(f, exp):
+ # First, we clamp exp to a reasonable range. The maximum range that we
+ # need is the largest range for an exponent, ([-127, 128] if you include
+ # inf and 0) plus the number of mantissa bits in either direction to
+ # account for denormals. This means that we need at least a range of
+ # [-150, 151]. For our implementation, however, what we really care
+ # about is that neither exp/2 nor exp-exp/2 go out of the regular range
+ # for floating-point exponents.
+ exp = ('imin', ('imax', exp, -252), 254)
+
+ # Now we compute two powers of 2, one for exp/2 and one for exp-exp/2.
+ # While the spec technically defines ldexp as f * 2.0^exp, simply
+ # multiplying once doesn't work when denormals are involved because
+ # 2.0^exp may not be representable even though ldexp(f, exp) is (see
+ # comments above about range). 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))
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