Squash_Decompress
Squash
» SWI Calls
» Squash_Decompress
Squash_Decompress
(SWI &42701)
Use Case 1 – bit 3 of R0 is set
| Entry | |
|---|---|
| R0 | Decompress Flags |
| R1 | Input size of file to be decompressed |
| -1 >= do not return maximum output size |
| Exit | |
|---|---|
| R0 | Required workspace size |
| R1 | Maximum output size (if requested), or -1 if not asked or unable to determine |
Use Case 2 – bit 3 of R0 is clear
| Entry | |
|---|---|
| R0 | Decompress Flags |
| R1 | Workspace pointer |
| R2 | Input pointer |
| R3 | Number of bytes of input available |
| R4 | Output pointer |
| R5 | Number of bytes of output space available |
| Exit | |
|---|---|
| R0 | Decompress Status |
| R1 | Preserved |
| R2 | Pointer to first unused input byte |
| R3 | Input bytes unused |
| R4 | Pointer to first unused output byte |
| R5 | Unused output space remaining |
Use
The purpose of this call is to provide lossless decompression.
Notes
Call this SWI initially with R0 = 8 and R1 = input file size, using the sizes it reports to allocate workspace and output buffers as appropriate. Note that the current algorithm always returns R1 = -1, so you must get this size by some other means. Then call repeatedly with R0 bit 3 clear until all the data is processed (as reported via the status bits returned in R0). If the input is exhausted (R3 < 12, R0 bit 1 set) the unused input must be resupplied.
If all the input data can be presented at once (R0 bits 0,1 clear) and the output buffer is large enough, a faster algorithm is used.
See also
Social
Follow us on
and
and
ROOL Store
Buy RISC OS Open merchandise here, including SD cards for Raspberry Pi and more.