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-rw-r--r--frontend/cspace_neon.S44
1 files changed, 28 insertions, 16 deletions
diff --git a/frontend/cspace_neon.S b/frontend/cspace_neon.S
index 8b201db..56ab304 100644
--- a/frontend/cspace_neon.S
+++ b/frontend/cspace_neon.S
@@ -27,19 +27,31 @@ FUNCTION(bgr555_to_rgb565): @ dst, src, bytes
blt btr16_end64
0:
pld [r1, #64*2]
+ @ Pulls 15-bit BGR color values (which are actually 16 bits) into q0-q3.
+ @ example: q0 = 0111 1110 0101 0011
vldmia r1!, {q0-q3}
- vshl.u16 q8, q0, #11
- vshl.u16 q9, q1, #11
- vshl.u16 q10, q2, #11
- vshl.u16 q11, q3, #11
- vsri.u16 q8, q0, #10
- vsri.u16 q9, q1, #10
- vsri.u16 q10, q2, #10
- vsri.u16 q11, q3, #10
+ @ Shift BGR color 1 bit to the left, discarding MSB and preparing for vbit.
+ @ MSB is used for transparency (not needed here, and can mess with green).
+ @ example: q0 = 1111 1100 1010 0110
vshl.u16 q0, q0, #1
vshl.u16 q1, q1, #1
vshl.u16 q2, q2, #1
vshl.u16 q3, q3, #1
+ @ Places red value in left most bits, clears bits to the right.
+ @ example: q8 = 1001 1000 0000 0000
+ vshl.u16 q8, q0, #10
+ vshl.u16 q9, q1, #10
+ vshl.u16 q10, q2, #10
+ vshl.u16 q11, q3, #10
+ @ Places blue value in right most bits, leaving bits to the left unchanged.
+ @ example: q8 = 1001 1000 0001 1111
+ vsri.u16 q8, q0, #11
+ vsri.u16 q9, q1, #11
+ vsri.u16 q10, q2, #11
+ vsri.u16 q11, q3, #11
+ @ Sets green value from shifted BGR color by apply a mask.
+ @ example: q15 = 0000 0111 1100 0000
+ @ q8 = 1001 1100 1001 1111
vbit q8, q0, q15
vbit q9, q1, q15
vbit q10, q2, q15
@@ -57,10 +69,10 @@ btr16_end64:
@ handle the remainder (reasonably rare)
0:
vld1.16 {q0}, [r1]!
- vshl.u16 q1, q0, #11
- vshl.u16 q2, q0, #1
- vsri.u16 q1, q0, #10
- vbit q1, q2, q15
+ vshl.u16 q0, q0, #1
+ vshl.u16 q1, q0, #10
+ vsri.u16 q1, q0, #11
+ vbit q1, q0, q15
subs r2, r2, #16
vst1.16 {q1}, [r0]!
bge 0b
@@ -73,10 +85,10 @@ btr16_end16:
@ very rare
vld1.16 {d0}, [r1]!
- vshl.u16 d1, d0, #11
- vshl.u16 d2, d0, #1
- vsri.u16 d1, d0, #10
- vbit d1, d2, d30
+ vshl.u16 d0, d0, #1
+ vshl.u16 d1, d0, #10
+ vsri.u16 d1, d0, #11
+ vbit d1, d0, d30
vst1.16 {d1}, [r0]!
bx lr