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Temporary fix for fgets() not using target-specific newline.

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This patch provides a temporary fix for the issue where the fgets()
function did not use the target-specific newline character to
decide if it has reached the end of the line. It defaulted to the
value $0a, which is the newline character on only some targets.
The Atari, for example, has newline character $9b instead.

This patch is ugly, because the ca65 assembler that is used for
fgets doesn't currently accept C-type character escape sequences
as values. Ideally we'd be able to write:

		cmp #'\n'

And this would end up being translated to a compare-immediate
to the target-specific newline character.

Since that is impossible, this patch substitutes the equivalent,
but ugly, code:

		.byte $c9, "\n"

This works because $c9 is the opcode for cmp #imm, and the "\n"
string /is/ translated to the platform-specific newline character,
at least when the 'string_escapes' feature is enabled.
This commit is contained in:
Sidney Cadot 2024-12-17 21:34:05 +01:00
parent a53524b9de
commit ceac9f87ba
1 changed files with 18 additions and 1 deletions
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19
libsrc/common/fgets.s
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@ -8,6 +8,8 @@
.import _fgetc, popptr1, pushptr1, popax, pushax, return0, ___errno .import _fgetc, popptr1, pushptr1, popax, pushax, return0, ___errno
.importzp ptr1, ptr4 .importzp ptr1, ptr4
.feature string_escapes
.include "errno.inc" .include "errno.inc"
.include "stdio.inc" .include "stdio.inc"
.include "_file.inc" .include "_file.inc"
@ -88,7 +90,22 @@ read_loop:
bne :+ bne :+
inc ptr4+1 inc ptr4+1
: cmp #$0A ; Stop at \n ; The next code line:
;
; .byte $c9, "\n"
;
; corresponds to a CMP #imm with the target-specific newline value as its operand.
; This works because (with the 'string_escapes' feature enabled), the "\n" string
; assembles to the target-specific value for the newline character.
;
; It would be better if we could just write:
;
; cmp #'\n'
;
; Unfortunately, ca65 doesn't currently handle escape characters in character
; constants. In the longer term, fixing that would be the preferred solution.
: .byte $c9, "\n" ; cmp #'\n'
beq done beq done
bne read_loop bne read_loop