1. (1 << (c - 1)) & ~((1 << c) - 1) is always zero. This together with
the fact that a square is always nonnegative (there's no overflow) allows
to remove a FFMAX.
2. The discriminant of the polynomial i * i - 2^(F+1) * i + 2^(F - 1) +
2^(2 * F) is negative; hence this polynomial has no real solutions, i.e.
its sign doesn't change and is always positive. This allows to remove a
FFMAX.
Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@gmail.com>
---
libavcodec/j2kenc.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/libavcodec/j2kenc.c b/libavcodec/j2kenc.c
index b5ac06b906..0a1421c844 100644
--- a/libavcodec/j2kenc.c
+++ b/libavcodec/j2kenc.c
@@ -522,13 +522,12 @@ static void init_luts(void)
for (i = 0; i < (1 << NMSEDEC_BITS); i++){
lut_nmsedec_sig[i] = FFMAX((6 * i - (9 << (NMSEDEC_FRACBITS - 1))) *
(1 << (12 - NMSEDEC_FRACBITS)), 0);
- lut_nmsedec_sig0[i] = FFMAX((i*i + (1<<NMSEDEC_FRACBITS-1) & mask) <<
1, 0);
+ lut_nmsedec_sig0[i] = 2 * i * i;
a = (i >> (NMSEDEC_BITS-2)&2) + 1;
lut_nmsedec_ref[i] = FFMAX((-2 * i + (1 << NMSEDEC_FRACBITS) + a * i
- (a * a << (NMSEDEC_FRACBITS - 2)))
* (1 << (13 - NMSEDEC_FRACBITS)), 0);
- lut_nmsedec_ref0[i] = FFMAX(((i * i - (i << (NMSEDEC_FRACBITS + 1)) +
(1 << (NMSEDEC_FRACBITS - 1)) + (1 << 2 * NMSEDEC_FRACBITS)) & mask)
- << 1, 0);
+ lut_nmsedec_ref0[i] = ((i * i - (i << (NMSEDEC_FRACBITS + 1)) + (1 <<
(NMSEDEC_FRACBITS - 1)) + (1 << 2 * NMSEDEC_FRACBITS)) & mask) << 1;
}
}
--
2.20.1
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