Implement ds align[alignment, offset]

include/asm/lexer.h

@@ -90,6 +90,11 @@ int yylex(void);
 bool lexer_CaptureRept(struct CaptureBody *capture);
 bool lexer_CaptureMacroBody(struct CaptureBody *capture);
 
+struct DsAlignment {
+	uint8_t alignment;
+	uint16_t alignOfs;
+};
+
 #define INITIAL_DS_ARG_SIZE 2
 struct DsArgList {
 	size_t nbArgs;

include/asm/section.h

@@ -53,6 +53,7 @@ void sect_EndLoadSection(void);
 struct Section *sect_GetSymbolSection(void);
 uint32_t sect_GetSymbolOffset(void);
 uint32_t sect_GetOutputOffset(void);
+uint32_t sect_GetAlignBytes(uint8_t alignment, uint16_t offset);
 void sect_AlignPC(uint8_t alignment, uint16_t offset);
 
 void sect_StartUnion(void);

man/rgbasm.5

@@ -647,8 +647,8 @@ is a shorthand for
 .Ic ALIGN Ns Bq Ar align , No 0 ) .
 This option can be used with
 .Bq Ar addr ,
-as long as they don't contradict eachother.
-It's also possible to request alignment in the middle of a section, see
+as long as they don't contradict each other.
+It's also possible to request alignment in the middle of a section; see
 .Sx Requesting alignment
 below.
 .El
@@ -824,7 +824,7 @@ or
 .Ic ROMX .
 .El
 .Pp
-Different declarations of the same unionized section are not appended, but instead overlaid on top of eachother, just like
+Different declarations of the same unionized section are not appended, but instead overlaid on top of each other, just like
 .Sx Unions .
 Similarly, the size of an unionized section is the largest of all its declarations.
 .Ss Section fragments
@@ -1398,6 +1398,16 @@ In ROM sections, it will be filled with the value passed to the
 .Fl p
 command-line option, except when using overlays with
 .Fl O .
+.Pp
+Instead of a specific number of bytes, you can specify
+.Ic DS ALIGN Ns Bq Ar align , offset
+to allocate however many bytes are required to align the subsequent data; see
+.Sx Requesting alignment
+below.
+(Note that
+.Ic ALIGN Ns Bq Ar align
+is a shorthand for
+.Ic ALIGN Ns Bq Ar align , No 0 ) .
 .Ss Defining constant data in ROM
 .Ic DB
 defines a list of bytes that will be stored in the final image.
@@ -2102,6 +2112,16 @@ Note that
 .Ic ALIGN Ar align
 is a shorthand for
 .Ic ALIGN Ar align , No 0 .
+.Pp
+There may be times when you don't just want to specify an alignment constraint at the current location, but also skip ahead until the constraint can be satisfied. In that case, you can use
+.Ic DS ALIGN Ns Bq Ar align , offset
+to allocate however many bytes are required to align the subsequent data.
+.Pp
+If the constraint cannot be met by skipping any amount of space, an error is produced.
+Note that
+.Ic ALIGN Ns Bq Ar align
+is a shorthand for
+.Ic ALIGN Ns Bq Ar align , No 0 .
 .Sh SEE ALSO
 .Xr rgbasm 1 ,
 .Xr rgblink 1 ,

src/asm/parser.y

@@ -509,6 +509,7 @@ enum {
 	struct SectionSpec sectSpec;
 	struct MacroArgs *macroArg;
 	enum AssertionType assertType;
+	struct DsAlignment dsAlign;
 	struct DsArgList dsArgs;
 	struct PurgeArgList purgeArgs;
 	struct {
@@ -664,6 +665,7 @@ enum {
 %type	<sectMod> sectmod
 %type	<macroArg> macroargs
 
+%type	<dsAlign> ds_align
 %type	<dsArgs> ds_args
 
 %type	<purgeArgs> purge_args
@@ -1169,6 +1171,40 @@ ds		: T_POP_DS uconst { sect_Skip($2, true); }
 			sect_RelBytes($2, $4.args, $4.nbArgs);
 			freeDsArgList(&$4);
 		}
+		| T_POP_DS ds_align trailing_comma {
+			uint32_t n = sect_GetAlignBytes($2.alignment, $2.alignOfs);
+
+			sect_Skip(n, true);
+			sect_AlignPC($2.alignment, $2.alignOfs);
+		}
+		| T_POP_DS ds_align T_COMMA ds_args trailing_comma {
+			uint32_t n = sect_GetAlignBytes($2.alignment, $2.alignOfs);
+
+			sect_RelBytes(n, $4.args, $4.nbArgs);
+			sect_AlignPC($2.alignment, $2.alignOfs);
+			freeDsArgList(&$4);
+		}
+;
+
+ds_align	: T_OP_ALIGN T_LBRACK uconst T_RBRACK {
+			if ($3 > 16) {
+				error("Alignment must be between 0 and 16, not %u\n", $3);
+			} else {
+				$$.alignment = $3;
+				$$.alignOfs = 0;
+			}
+		}
+		| T_OP_ALIGN T_LBRACK uconst T_COMMA uconst T_RBRACK {
+			if ($3 > 16) {
+				error("Alignment must be between 0 and 16, not %u\n", $3);
+			} else if ($5 >= 1 << $3) {
+				error("Offset must be between 0 and %u, not %u\n",
+					(1 << $3) - 1, $5);
+			} else {
+				$$.alignment = $3;
+				$$.alignOfs = $5;
+			}
+		}
 ;
 
 ds_args		: reloc_8bit {

src/asm/section.c

@@ -477,6 +477,21 @@ uint32_t sect_GetOutputOffset(void)
 	return curOffset + loadOffset;
 }
 
+// Returns how many bytes need outputting for the specified alignment and offset to succeed
+uint32_t sect_GetAlignBytes(uint8_t alignment, uint16_t offset)
+{
+	struct Section *sect = sect_GetSymbolSection();
+
+	// If the section is undefined, or not fixed and not aligned, no bytes are needed
+	if (!sect || (sect->org == (uint32_t)-1 && sect->align == 0))
+		return 0;
+
+	uint32_t pcValue = sect->org != (uint32_t)-1 ? sym_GetPCValue() : sect->align != 0
+		? (sect->alignOfs + curOffset) % (1 << sect->align) : 0;
+	// We need `(pcValue + return value) % (1 << alignment) == offset
+	return (offset - pcValue) % (1 << alignment);
+}
+
 void sect_AlignPC(uint8_t alignment, uint16_t offset)
 {
 	if (!checksection())
@@ -489,15 +504,11 @@ void sect_AlignPC(uint8_t alignment, uint16_t offset)
 		if ((sym_GetPCValue() - offset) % alignSize)
 			error("Section's fixed address fails required alignment (PC = $%04" PRIx32
 			      ")\n", sym_GetPCValue());
-	} else if (sect->align != 0) {
-		if ((((sect->alignOfs + curOffset) % (1 << sect->align)) - offset) % alignSize) {
-			error("Section's alignment fails required alignment (offset from section start = $%04"
-				PRIx32 ")\n", curOffset);
-		} else if (alignment > sect->align) {
-			sect->align = alignment;
-			sect->alignOfs = (offset - curOffset) % alignSize;
-		}
-	} else {
+	} else if (sect->align != 0 && (((sect->alignOfs + curOffset) % (1 << sect->align))
+					- offset) % alignSize) {
+		error("Section's alignment fails required alignment (offset from section start = $%04"
+			PRIx32 ")\n", curOffset);
+	} else if (alignment > sect->align) {
 		sect->align = alignment;
 		// We need `(sect->alignOfs + curOffset) % alignSize == offset
 		sect->alignOfs = (offset - curOffset) % alignSize;

test/asm/ds-align.asm

@@ -0,0 +1,22 @@
+SECTION "aligned", ROM0, ALIGN[8]
+db 1, 2, 3, 4, 5 ; five
+ds align[8, $ff], 6 ; (1 << 8) - five - one = 250 bytes
+db 7 ; one
+align 8
+
+SECTION "fixed", ROM0[$100]
+ds align[2] ; already aligned, 0 bytes
+db 8, 9, 10
+ds align[4, $e], 11 ; (1 << 4) - three - two = 11 bytes
+db 12, 13 ; two
+align 4
+
+SECTION "floating", ROM0
+db 14, 15 ; two
+ds align[4] ; not aligned, 0 bytes
+align 4
+db 16, 17, 18 ; three
+align 4, 3
+ds align[5], 19, 20 ; (1 << 5) - three = 29 bytes
+db 21 ; one
+align 5, 1