ref: 7b098ae8c62f5910a748d57530b3ce4568ed5eb5
dir: /src/arm/64/cdef.S/
/*
* Copyright © 2018, VideoLAN and dav1d authors
* Copyright © 2019, Martin Storsjo
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "src/arm/asm.S"
#include "util.S"
.macro pad_top_bottom s1, s2, w, stride, rn, rw, ret
tst w6, #1 // CDEF_HAVE_LEFT
b.eq 2f
// CDEF_HAVE_LEFT
sub \s1, \s1, #2
sub \s2, \s2, #2
tst w6, #2 // CDEF_HAVE_RIGHT
b.eq 1f
// CDEF_HAVE_LEFT+CDEF_HAVE_RIGHT
ldr \rn\()0, [\s1]
ldr s1, [\s1, #\w]
ldr \rn\()2, [\s2]
ldr s3, [\s2, #\w]
uxtl v0.8h, v0.8b
uxtl v1.8h, v1.8b
uxtl v2.8h, v2.8b
uxtl v3.8h, v3.8b
str \rw\()0, [x0]
str d1, [x0, #2*\w]
add x0, x0, #2*\stride
str \rw\()2, [x0]
str d3, [x0, #2*\w]
.if \ret
ret
.else
add x0, x0, #2*\stride
b 3f
.endif
1:
// CDEF_HAVE_LEFT+!CDEF_HAVE_RIGHT
ldr \rn\()0, [\s1]
ldr h1, [\s1, #\w]
ldr \rn\()2, [\s2]
ldr h3, [\s2, #\w]
uxtl v0.8h, v0.8b
uxtl v1.8h, v1.8b
uxtl v2.8h, v2.8b
uxtl v3.8h, v3.8b
str \rw\()0, [x0]
str s1, [x0, #2*\w]
str s31, [x0, #2*\w+4]
add x0, x0, #2*\stride
str \rw\()2, [x0]
str s3, [x0, #2*\w]
str s31, [x0, #2*\w+4]
.if \ret
ret
.else
add x0, x0, #2*\stride
b 3f
.endif
2:
// !CDEF_HAVE_LEFT
tst w6, #2 // CDEF_HAVE_RIGHT
b.eq 1f
// !CDEF_HAVE_LEFT+CDEF_HAVE_RIGHT
ldr \rn\()0, [\s1]
ldr h1, [\s1, #\w]
ldr \rn\()2, [\s2]
ldr h3, [\s2, #\w]
uxtl v0.8h, v0.8b
uxtl v1.8h, v1.8b
uxtl v2.8h, v2.8b
uxtl v3.8h, v3.8b
str s31, [x0]
stur \rw\()0, [x0, #4]
str s1, [x0, #4+2*\w]
add x0, x0, #2*\stride
str s31, [x0]
stur \rw\()2, [x0, #4]
str s3, [x0, #4+2*\w]
.if \ret
ret
.else
add x0, x0, #2*\stride
b 3f
.endif
1:
// !CDEF_HAVE_LEFT+!CDEF_HAVE_RIGHT
ldr \rn\()0, [\s1]
ldr \rn\()1, [\s2]
uxtl v0.8h, v0.8b
uxtl v1.8h, v1.8b
str s31, [x0]
stur \rw\()0, [x0, #4]
str s31, [x0, #4+2*\w]
add x0, x0, #2*\stride
str s31, [x0]
stur \rw\()1, [x0, #4]
str s31, [x0, #4+2*\w]
.if \ret
ret
.else
add x0, x0, #2*\stride
.endif
3:
.endm
// void dav1d_cdef_paddingX_neon(uint16_t *tmp, const pixel *src,
// ptrdiff_t src_stride, const pixel (*left)[2],
// /*const*/ pixel *const top[2], int h,
// enum CdefEdgeFlags edges);
.macro padding_func w, stride, rn, rw
function cdef_padding\w\()_neon, export=1
movi v30.16b, #255
ushr v30.8h, v30.8h, #1 // INT16_MAX
mov v31.16b, v30.16b
sub x0, x0, #2*(2*\stride+2)
tst w6, #4 // CDEF_HAVE_TOP
b.ne 1f
// !CDEF_HAVE_TOP
st1 {v30.8h, v31.8h}, [x0], #32
.if \w == 8
st1 {v30.8h, v31.8h}, [x0], #32
.endif
b 3f
1:
// CDEF_HAVE_TOP
ldr x8, [x4]
ldr x9, [x4, #8]
pad_top_bottom x8, x9, \w, \stride, \rn, \rw, 0
// Middle section
3:
tst w6, #1 // CDEF_HAVE_LEFT
b.eq 2f
// CDEF_HAVE_LEFT
tst w6, #2 // CDEF_HAVE_RIGHT
b.eq 1f
// CDEF_HAVE_LEFT+CDEF_HAVE_RIGHT
0:
ld1 {v0.h}[0], [x3], #2
ldr \rn\()1, [x1]
ldr h2, [x1, #\w]
add x1, x1, x2
subs w5, w5, #1
uxtl v0.8h, v0.8b
uxtl v1.8h, v1.8b
uxtl v2.8h, v2.8b
str s0, [x0]
stur \rw\()1, [x0, #4]
str s2, [x0, #4+2*\w]
add x0, x0, #2*\stride
b.gt 0b
b 3f
1:
// CDEF_HAVE_LEFT+!CDEF_HAVE_RIGHT
ld1 {v0.h}[0], [x3], #2
.if \w == 8
ld1 {v1.8b}, [x1], x2
.else
ld1 {v1.s}[0], [x1], x2
.endif
subs w5, w5, #1
uxtl v0.8h, v0.8b
uxtl v1.8h, v1.8b
str s0, [x0]
stur \rw\()1, [x0, #4]
str s31, [x0, #4+2*\w]
add x0, x0, #2*\stride
b.gt 1b
b 3f
2:
tst w6, #2 // CDEF_HAVE_RIGHT
b.eq 1f
// !CDEF_HAVE_LEFT+CDEF_HAVE_RIGHT
0:
ldr \rn\()0, [x1]
ldr h1, [x1, #\w]
add x1, x1, x2
subs w5, w5, #1
uxtl v0.8h, v0.8b
uxtl v1.8h, v1.8b
str s31, [x0]
stur \rw\()0, [x0, #4]
str s1, [x0, #4+2*\w]
add x0, x0, #2*\stride
b.gt 0b
b 3f
1:
// !CDEF_HAVE_LEFT+!CDEF_HAVE_RIGHT
.if \w == 8
ld1 {v0.8b}, [x1], x2
.else
ld1 {v0.s}[0], [x1], x2
.endif
subs w5, w5, #1
uxtl v0.8h, v0.8b
str s31, [x0]
stur \rw\()0, [x0, #4]
str s31, [x0, #4+2*\w]
add x0, x0, #2*\stride
b.gt 1b
3:
tst w6, #8 // CDEF_HAVE_BOTTOM
b.ne 1f
// !CDEF_HAVE_BOTTOM
st1 {v30.8h, v31.8h}, [x0], #32
.if \w == 8
st1 {v30.8h, v31.8h}, [x0], #32
.endif
ret
1:
// CDEF_HAVE_BOTTOM
add x9, x1, x2
pad_top_bottom x1, x9, \w, \stride, \rn, \rw, 1
endfunc
.endm
padding_func 8, 16, d, q
padding_func 4, 8, s, d
.macro dir_table w, stride
const directions\w
.byte -1 * \stride + 1, -2 * \stride + 2
.byte 0 * \stride + 1, -1 * \stride + 2
.byte 0 * \stride + 1, 0 * \stride + 2
.byte 0 * \stride + 1, 1 * \stride + 2
.byte 1 * \stride + 1, 2 * \stride + 2
.byte 1 * \stride + 0, 2 * \stride + 1
.byte 1 * \stride + 0, 2 * \stride + 0
.byte 1 * \stride + 0, 2 * \stride - 1
// Repeated, to avoid & 7
.byte -1 * \stride + 1, -2 * \stride + 2
.byte 0 * \stride + 1, -1 * \stride + 2
.byte 0 * \stride + 1, 0 * \stride + 2
.byte 0 * \stride + 1, 1 * \stride + 2
.byte 1 * \stride + 1, 2 * \stride + 2
.byte 1 * \stride + 0, 2 * \stride + 1
endconst
.endm
dir_table 8, 16
dir_table 4, 8
const pri_taps
.byte 4, 2, 3, 3
endconst
.macro load_px d1, d2, w
.if \w == 8
add x6, x2, w9, sxtb #1 // x + off
sub x9, x2, w9, sxtb #1 // x - off
ld1 {\d1\().8h}, [x6] // p0
ld1 {\d2\().8h}, [x9] // p1
.else
add x6, x2, w9, sxtb #1 // x + off
sub x9, x2, w9, sxtb #1 // x - off
ld1 {\d1\().4h}, [x6] // p0
add x6, x6, #2*8 // += stride
ld1 {\d2\().4h}, [x9] // p1
add x9, x9, #2*8 // += stride
ld1 {\d1\().d}[1], [x6] // p0
ld1 {\d2\().d}[1], [x9] // p1
.endif
.endm
.macro handle_pixel s1, s2, threshold, thresh_vec, shift, tap
cmeq v16.8h, \s1\().8h, v31.8h
cmeq v17.8h, \s2\().8h, v31.8h
bic v16.16b, \s1\().16b, v16.16b
bic v17.16b, \s2\().16b, v17.16b
umin v2.8h, v2.8h, \s1\().8h
umax v3.8h, v3.8h, v16.8h
umin v2.8h, v2.8h, \s2\().8h
umax v3.8h, v3.8h, v17.8h
cbz \threshold, 3f
uabd v16.8h, v0.8h, \s1\().8h // abs(diff)
uabd v20.8h, v0.8h, \s2\().8h // abs(diff)
ushl v17.8h, v16.8h, \shift // abs(diff) >> shift
ushl v21.8h, v20.8h, \shift // abs(diff) >> shift
sub v17.8h, \thresh_vec, v17.8h // threshold - (abs(diff) >> shift)
sub v21.8h, \thresh_vec, v21.8h // threshold - (abs(diff) >> shift)
smax v17.8h, v29.8h, v17.8h // imax(0, threshold - ())
smax v21.8h, v29.8h, v21.8h // imax(0, threshold - ())
cmhi v18.8h, v0.8h, \s1\().8h // px > p0
cmhi v22.8h, v0.8h, \s2\().8h // px > p1
smin v17.8h, v17.8h, v16.8h // imin(abs(diff), imax())
smin v21.8h, v21.8h, v20.8h // imin(abs(diff), imax())
dup v19.8h, \tap // taps[k]/taps[k]
neg v16.8h, v17.8h // -imin()
neg v20.8h, v21.8h // -imin()
bsl v18.16b, v16.16b, v17.16b // constrain() = apply_sign()
bsl v22.16b, v20.16b, v21.16b // constrain() = apply_sign()
mla v1.8h, v18.8h, v19.8h // sum += taps[k] * constrain()
mla v1.8h, v22.8h, v19.8h // sum += taps[k] * constrain()
3:
.endm
// void dav1d_cdef_filterX_neon(pixel *dst, ptrdiff_t dst_stride,
// const uint16_t *tmp, int pri_strength,
// int sec_strength, int dir, int damping, int h);
.macro filter w
function cdef_filter\w\()_neon, export=1
movrel x8, pri_taps
and w9, w3, #1
add x8, x8, w9, uxtw #1
movrel x9, directions\w
add x5, x9, w5, uxtw #1
movi v31.16b, #255
movi v30.8h, #15
movi v29.8h, #0
dup v28.8h, w6 // damping
ushr v31.8h, v31.8h, #1 // INT16_MAX
dup v25.8h, w3 // threshold
dup v27.8h, w4 // threshold
clz v24.8h, v25.8h // clz(threshold)
clz v26.8h, v27.8h // clz(threshold)
sub v24.8h, v30.8h, v24.8h // ulog2(threshold)
sub v26.8h, v30.8h, v26.8h // ulog2(threshold)
sub v24.8h, v28.8h, v24.8h // damping - ulog2(threshold)
sub v26.8h, v28.8h, v26.8h // damping - ulog2(threshold)
smax v24.8h, v29.8h, v24.8h // shift = imax(0, damping - ulog2(threshold))
smax v26.8h, v29.8h, v26.8h // shift = imax(0, damping - ulog2(threshold))
neg v24.8h, v24.8h // -shift
neg v26.8h, v26.8h // -shift
1:
.if \w == 8
ld1 {v0.8h}, [x2] // px
.else
add x12, x2, #2*8
ld1 {v0.4h}, [x2] // px
ld1 {v0.d}[1], [x12] // px
.endif
movi v1.8h, #0 // sum
mov v2.16b, v0.16b // min
mov v3.16b, v0.16b // max
// Instead of loading sec_taps 2, 1 from memory, just set it
// to 2 initially and decrease for the second round.
mov w11, #2 // sec_taps[0]
2:
ldrb w9, [x5] // off1
load_px v4, v5, \w
add x5, x5, #4 // +2*2
ldrb w9, [x5] // off2
load_px v6, v7, \w
ldrb w10, [x8] // *pri_taps
handle_pixel v4, v5, w3, v25.8h, v24.8h, w10
add x5, x5, #8 // +2*4
ldrb w9, [x5] // off3
load_px v4, v5, \w
handle_pixel v6, v7, w4, v27.8h, v26.8h, w11
handle_pixel v4, v5, w4, v27.8h, v26.8h, w11
sub x5, x5, #11 // x8 -= 2*(2+4); x8 += 1;
subs w11, w11, #1 // sec_tap-- (value)
add x8, x8, #1 // pri_taps++ (pointer)
b.ne 2b
sshr v4.8h, v1.8h, #15 // -(sum < 0)
add v1.8h, v1.8h, v4.8h // sum - (sum < 0)
srshr v1.8h, v1.8h, #4 // (8 + sum - (sum < 0)) >> 4
add v0.8h, v0.8h, v1.8h // px + (8 + sum ...) >> 4
smin v0.8h, v0.8h, v3.8h
smax v0.8h, v0.8h, v2.8h // iclip(px + .., min, max)
xtn v0.8b, v0.8h
.if \w == 8
add x2, x2, #2*16 // tmp += tmp_stride
subs w7, w7, #1 // h--
st1 {v0.8b}, [x0], x1
.else
st1 {v0.s}[0], [x0], x1
add x2, x2, #2*16 // tmp += 2*tmp_stride
subs w7, w7, #2 // h -= 2
st1 {v0.s}[1], [x0], x1
.endif
// Reset pri_taps/sec_taps back to the original point
sub x5, x5, #2
sub x8, x8, #2
b.gt 1b
ret
endfunc
.endm
filter 8
filter 4
const div_table
.short 840, 420, 280, 210, 168, 140, 120, 105
endconst
const alt_fact
.short 420, 210, 140, 105, 105, 105, 105, 105, 140, 210, 420, 0
endconst
// int dav1d_cdef_find_dir_neon(const pixel *img, const ptrdiff_t stride,
// unsigned *const var)
function cdef_find_dir_neon, export=1
sub sp, sp, #32 // cost
mov w3, #8
movi v31.16b, #128
movi v30.16b, #0
movi v1.8h, #0 // v0-v1 sum_diag[0]
movi v3.8h, #0 // v2-v3 sum_diag[1]
movi v5.8h, #0 // v4-v5 sum_hv[0-1]
movi v7.8h, #0 // v6-v7 sum_alt[0]
movi v17.8h, #0 // v16-v17 sum_alt[1]
movi v18.8h, #0 // v18-v19 sum_alt[2]
movi v19.8h, #0
movi v21.8h, #0 // v20-v21 sum_alt[3]
.irpc i, 01234567
ld1 {v26.8b}, [x0], x1
usubl v26.8h, v26.8b, v31.8b
addv h25, v26.8h // [y]
rev64 v27.8h, v26.8h
addp v28.8h, v26.8h, v30.8h // [(x >> 1)]
add v5.8h, v5.8h, v26.8h // sum_hv[1]
ext v27.16b, v27.16b, v27.16b, #8 // [-x]
rev64 v29.4h, v28.4h // [-(x >> 1)]
ins v4.h[\i], v25.h[0] // sum_hv[0]
.if \i == 0
mov v0.16b, v26.16b // sum_diag[0]
mov v2.16b, v27.16b // sum_diag[1]
mov v6.16b, v28.16b // sum_alt[0]
mov v16.16b, v29.16b // sum_alt[1]
.else
ext v22.16b, v30.16b, v26.16b, #(16-2*\i)
ext v23.16b, v26.16b, v30.16b, #(16-2*\i)
ext v24.16b, v30.16b, v27.16b, #(16-2*\i)
ext v25.16b, v27.16b, v30.16b, #(16-2*\i)
add v0.8h, v0.8h, v22.8h // sum_diag[0]
add v1.8h, v1.8h, v23.8h // sum_diag[0]
add v2.8h, v2.8h, v24.8h // sum_diag[1]
add v3.8h, v3.8h, v25.8h // sum_diag[1]
ext v22.16b, v30.16b, v28.16b, #(16-2*\i)
ext v23.16b, v28.16b, v30.16b, #(16-2*\i)
ext v24.16b, v30.16b, v29.16b, #(16-2*\i)
ext v25.16b, v29.16b, v30.16b, #(16-2*\i)
add v6.8h, v6.8h, v22.8h // sum_alt[0]
add v7.8h, v7.8h, v23.8h // sum_alt[0]
add v16.8h, v16.8h, v24.8h // sum_alt[1]
add v17.8h, v17.8h, v25.8h // sum_alt[1]
.endif
.if \i < 6
ext v22.16b, v30.16b, v26.16b, #(16-2*(3-(\i/2)))
ext v23.16b, v26.16b, v30.16b, #(16-2*(3-(\i/2)))
add v18.8h, v18.8h, v22.8h // sum_alt[2]
add v19.8h, v19.8h, v23.8h // sum_alt[2]
.else
add v18.8h, v18.8h, v26.8h // sum_alt[2]
.endif
.if \i == 0
mov v20.16b, v26.16b // sum_alt[3]
.elseif \i == 1
add v20.8h, v20.8h, v26.8h // sum_alt[3]
.else
ext v24.16b, v30.16b, v26.16b, #(16-2*(\i/2))
ext v25.16b, v26.16b, v30.16b, #(16-2*(\i/2))
add v20.8h, v20.8h, v24.8h // sum_alt[3]
add v21.8h, v21.8h, v25.8h // sum_alt[3]
.endif
.endr
movi v31.4s, #105
smull v26.4s, v4.4h, v4.4h // sum_hv[0]*sum_hv[0]
smlal2 v26.4s, v4.8h, v4.8h
smull v27.4s, v5.4h, v5.4h // sum_hv[1]*sum_hv[1]
smlal2 v27.4s, v5.8h, v5.8h
mul v26.4s, v26.4s, v31.4s // cost[2] *= 105
mul v27.4s, v27.4s, v31.4s // cost[6] *= 105
addv s4, v26.4s // cost[2]
addv s5, v27.4s // cost[6]
rev64 v1.8h, v1.8h
rev64 v3.8h, v3.8h
ext v1.16b, v1.16b, v1.16b, #8 // sum_diag[0][15-n]
ext v3.16b, v3.16b, v3.16b, #8 // sum_diag[1][15-n]
ext v1.16b, v1.16b, v1.16b, #2 // sum_diag[0][14-n]
ext v3.16b, v3.16b, v3.16b, #2 // sum_diag[1][14-n]
str s4, [sp, #2*4] // cost[2]
str s5, [sp, #6*4] // cost[6]
movrel x4, div_table
ld1 {v31.8h}, [x4]
smull v22.4s, v0.4h, v0.4h // sum_diag[0]*sum_diag[0]
smull2 v23.4s, v0.8h, v0.8h
smlal v22.4s, v1.4h, v1.4h
smlal2 v23.4s, v1.8h, v1.8h
smull v24.4s, v2.4h, v2.4h // sum_diag[1]*sum_diag[1]
smull2 v25.4s, v2.8h, v2.8h
smlal v24.4s, v3.4h, v3.4h
smlal2 v25.4s, v3.8h, v3.8h
uxtl v30.4s, v31.4h // div_table
uxtl2 v31.4s, v31.8h
mul v22.4s, v22.4s, v30.4s // cost[0]
mla v22.4s, v23.4s, v31.4s // cost[0]
mul v24.4s, v24.4s, v30.4s // cost[4]
mla v24.4s, v25.4s, v31.4s // cost[4]
addv s0, v22.4s // cost[0]
addv s2, v24.4s // cost[4]
movrel x5, alt_fact
ld1 {v29.4h, v30.4h, v31.4h}, [x5]// div_table[2*m+1] + 105
str s0, [sp, #0*4] // cost[0]
str s2, [sp, #4*4] // cost[4]
uxtl v29.4s, v29.4h // div_table[2*m+1] + 105
uxtl v30.4s, v30.4h
uxtl v31.4s, v31.4h
.macro cost_alt d1, d2, s1, s2, s3, s4
smull v22.4s, \s1\().4h, \s1\().4h // sum_alt[n]*sum_alt[n]
smull2 v23.4s, \s1\().8h, \s1\().8h
smull v24.4s, \s2\().4h, \s2\().4h
smull v25.4s, \s3\().4h, \s3\().4h // sum_alt[n]*sum_alt[n]
smull2 v26.4s, \s3\().8h, \s3\().8h
smull v27.4s, \s4\().4h, \s4\().4h
mul v22.4s, v22.4s, v29.4s // sum_alt[n]^2*fact
mla v22.4s, v23.4s, v30.4s
mla v22.4s, v24.4s, v31.4s
mul v25.4s, v25.4s, v29.4s // sum_alt[n]^2*fact
mla v25.4s, v26.4s, v30.4s
mla v25.4s, v27.4s, v31.4s
addv \d1, v22.4s // *cost_ptr
addv \d2, v25.4s // *cost_ptr
.endm
cost_alt s6, s16, v6, v7, v16, v17 // cost[1], cost[3]
str s6, [sp, #1*4] // cost[1]
str s16, [sp, #3*4] // cost[3]
cost_alt s18, s20, v18, v19, v20, v21 // cost[5], cost[7]
str s18, [sp, #5*4] // cost[5]
str s20, [sp, #7*4] // cost[7]
mov w0, #0 // best_dir
mov w1, v0.s[0] // best_cost
mov w3, #1 // n
mov w4, v6.s[0]
.macro find_best s1, s2, s3
.ifnb \s2
mov w5, \s2\().s[0]
.endif
cmp w4, w1 // cost[n] > best_cost
csel w0, w3, w0, gt // best_dir = n
csel w1, w4, w1, gt // best_cost = cost[n]
.ifnb \s2
add w3, w3, #1 // n++
cmp w5, w1 // cost[n] > best_cost
mov w4, \s3\().s[0]
csel w0, w3, w0, gt // best_dir = n
csel w1, w5, w1, gt // best_cost = cost[n]
add w3, w3, #1 // n++
.endif
.endm
find_best v6, v4, v16
find_best v16, v2, v18
find_best v18, v5, v20
find_best v20
eor w3, w0, #4 // best_dir ^4
ldr w4, [sp, w3, uxtw #2]
sub w1, w1, w4 // best_cost - cost[best_dir ^ 4]
lsr w1, w1, #10
str w1, [x2] // *var
add sp, sp, #32
ret
endfunc