6502/PLASMA
1
0
Fork 0
mirror of https://github.com/dschmenk/PLASMA.git synced 2024-07-03 05:29:30 +00:00
Code Issues Projects Releases Wiki Activity

Add STRUC explanation and fix multidimensional array

Browse Source
This commit is contained in:
David Schmenk 2014-11-25 10:58:51 -08:00
parent c3019689e2
commit dc2c7f1b4e
1 changed files with 36 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

48
doc/User Manual.md
View File

@ -234,7 +234,7 @@ def hgrfill(val)
for yscan = 0 to 191
for xscan = 0 to 19
hgrscan:[yscan][xscan] = val
hgrscan:[yscan, xscan] = val
next
next
end
@ -246,7 +246,7 @@ def hgrfill(val)
for yscan = 0 to 191
for xscan = 0 to 39
hgrscan.[yscan][xscan] = val
hgrscan.[yscan, xscan] = val
next
next
end
@ -262,10 +262,31 @@ word = 2
byte = "PLASMA"
puti(myrec:0) // ID = 2
putc($8D) // Carriage return
puti(myrec.2) // Name length = 6 (Pascal string puts length byte first)
```
This contrived example shows how one can access offsets from a variable as either `byte`s or `word`s regardless of how they were defined. This operator becomes more powerful when combined with pointers, defined next.
#### Defining Structures
Structures can be defined so that the offsets are calculated for you. The previous example can be written as:
```
predef puti // print an integer
struc mystruc // mystruc will be defined as the size of the structure itself
word id
byte name // one byte for length, the number of characters are variable
end
byte myrec[]
word = 2
byte = "PLASMA"
puti(mystruc) // This will print '3', the size of the structure as defined
putc($8D) // Carriage return
puti(myrec:id) // ID = 2
putc($8D) // Carriage return
puti(myrec.name) // Name length = 6 (Pascal string puts length byte first)
```
#### Pointers
Pointers are values that represent addresses. In order to get the value pointed to by the address, one must 'dereference' the pointer. All data and code memory has a unique address, all 65536 of them (16 bits). In the Apple II, many addresses are actually connected to hardware instead of memory. Accessing these addresses can make thing happen in the Apple II, or read external inputs like the keyboard and joystick.
@ -282,24 +303,27 @@ end
```
Pointers to structures or arrays can be referenced with the `->` and `=>` operators, pointing to `byte` or `word` sized elements.
```
const elem_id = 0
const elem_addr = 1
struc record
byte id
word addr
end
def addentry(entry, id, addr)
entry->elem_id = id // set ID byte
entry=>elem_addr = addr // set address
return entry + 3 // return next enry address
def addentry(entry, new_id, new_addr)
entry->id = new_id // set ID (byte)
entry=>addr = new_addr // set address (word)
return entry + record // return next enry address
end
```
The above is equivalent to:
```
const elem_id = 0
const elem_addr = 1
const record_size = 3
def addentry(entry, id, addr)
(entry).elem_id = id // set ID byte
(entry):elem_addr = addr // set address
return entry + 3 // return next enry address
def addentry(entry, new_id, new_addr)
(entry).elem_id = new_id // set ID byte
(entry):elem_addr = new_addr // set address
return entry + record_size // return next enry address
end
```