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authorRangi <35663410+Rangi42@users.noreply.github.com>2020-07-07 19:48:22 -0400
committerGitHub <noreply@github.com>2020-07-07 19:48:22 -0400
commit9571c550b6a0dcb3a4f54513c881661a87271024 (patch)
treed73507228a57e4f3cece2fb93fe7df3a9439553f /home/count_set_bits.asm
parentc480632d5494d04f7f5f0298a31877a2293b564e (diff)
parentbbf2f51a02b2544f1bef32a5868503b474ae2fef (diff)
Merge pull request #263 from Rangi42/master
Syncing style with pokecrystal
Diffstat (limited to 'home/count_set_bits.asm')
-rw-r--r--home/count_set_bits.asm24
1 files changed, 24 insertions, 0 deletions
diff --git a/home/count_set_bits.asm b/home/count_set_bits.asm
new file mode 100644
index 00000000..73f7fa9c
--- /dev/null
+++ b/home/count_set_bits.asm
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+; function to count how many bits are set in a string of bytes
+; INPUT:
+; hl = address of string of bytes
+; b = length of string of bytes
+; OUTPUT:
+; [wNumSetBits] = number of set bits
+CountSetBits::
+ ld c, 0
+.loop
+ ld a, [hli]
+ ld e, a
+ ld d, 8
+.innerLoop ; count how many bits are set in the current byte
+ srl e
+ ld a, 0
+ adc c
+ ld c, a
+ dec d
+ jr nz, .innerLoop
+ dec b
+ jr nz, .loop
+ ld a, c
+ ld [wNumSetBits], a
+ ret