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author | Dave Chapman <dave@dchapman.com> | 2006-02-03 08:27:53 +0000 |
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committer | Dave Chapman <dave@dchapman.com> | 2006-02-03 08:27:53 +0000 |
commit | 347992e9d93ed0f91cde7e2d580cfdc8d5eb95f4 (patch) | |
tree | 631dade87e98ef745730460067f7560919dae459 /apps/codecs/libalac/alac.c | |
parent | d2e75bf02d1ad91fca0e283e8c71b1091ec85a80 (diff) | |
download | rockbox-347992e9d93ed0f91cde7e2d580cfdc8d5eb95f4.tar.gz rockbox-347992e9d93ed0f91cde7e2d580cfdc8d5eb95f4.zip |
Optimised C version of count_leading_zeros() taken from alac-0.1.1. This makes ALAC very close to realtime on the ipod (just the very occasional skip during disk reading - it is realtime when the disk is sleeping).
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@8545 a1c6a512-1295-4272-9138-f99709370657
Diffstat (limited to 'apps/codecs/libalac/alac.c')
-rw-r--r-- | apps/codecs/libalac/alac.c | 48 |
1 files changed, 39 insertions, 9 deletions
diff --git a/apps/codecs/libalac/alac.c b/apps/codecs/libalac/alac.c index 638ca93c16..0082b6dd42 100644 --- a/apps/codecs/libalac/alac.c +++ b/apps/codecs/libalac/alac.c | |||
@@ -184,18 +184,48 @@ static inline void unreadbits(alac_file *alac, int bits) | |||
184 | alac->input_buffer_bitaccumulator *= -1; | 184 | alac->input_buffer_bitaccumulator *= -1; |
185 | } | 185 | } |
186 | 186 | ||
187 | /* hideously inefficient. could use a bitmask search, | 187 | static inline int count_leading_zeros(int input) |
188 | * alternatively bsr on x86, | ||
189 | */ | ||
190 | static inline int count_leading_zeros(int32_t input) | ||
191 | { | 188 | { |
192 | int i = 0; | 189 | int output = 0; |
193 | while (!(0x80000000 & input) && i < 32) | 190 | int curbyte = 0; |
191 | |||
192 | curbyte = input >> 24; | ||
193 | if (curbyte) goto found; | ||
194 | output += 8; | ||
195 | |||
196 | curbyte = input >> 16; | ||
197 | if (curbyte & 0xff) goto found; | ||
198 | output += 8; | ||
199 | |||
200 | curbyte = input >> 8; | ||
201 | if (curbyte & 0xff) goto found; | ||
202 | output += 8; | ||
203 | |||
204 | curbyte = input; | ||
205 | if (curbyte & 0xff) goto found; | ||
206 | output += 8; | ||
207 | |||
208 | return output; | ||
209 | |||
210 | found: | ||
211 | if (!(curbyte & 0xf0)) | ||
194 | { | 212 | { |
195 | i++; | 213 | output += 4; |
196 | input = input << 1; | ||
197 | } | 214 | } |
198 | return i; | 215 | else |
216 | curbyte >>= 4; | ||
217 | |||
218 | if (curbyte & 0x8) | ||
219 | return output; | ||
220 | if (curbyte & 0x4) | ||
221 | return output + 1; | ||
222 | if (curbyte & 0x2) | ||
223 | return output + 2; | ||
224 | if (curbyte & 0x1) | ||
225 | return output + 3; | ||
226 | |||
227 | /* shouldn't get here: */ | ||
228 | return output + 4; | ||
199 | } | 229 | } |
200 | 230 | ||
201 | void basterdised_rice_decompress(alac_file *alac, | 231 | void basterdised_rice_decompress(alac_file *alac, |