Implement ds align[alignment, offset] (#1181)

test/asm/ds-align-min.asm

@@ -0,0 +1,7 @@
+SECTION "test", ROM0
+align 3 ; 3 < 4, so this is used in `ds align` below
+db 1, 2, 5 ; three
+ds align[4] ; (1 << 3) - three = 5 bytes
+db 10, 20 ; two
+align 4, 2
+assert @ - STARTOF("test") == 3 + 5 + 2

test/asm/ds-align-offset.asm

@@ -0,0 +1,7 @@
+SECTION "test", ROM0
+align 3, 3 ; 3 < 4, so this is used in `ds align` below
+db 2, 22, 222 ; three
+ds align[4, 4] ; (1 << 3) - 3 - three + 4 = 6 bytes
+db 42 ; one
+align 4, 5
+assert @ - STARTOF("test") == 3 + 6 + 1

test/asm/ds-align.asm

@@ -0,0 +1,25 @@
+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
+assert @ - STARTOF("aligned") == 5 + 250 + 1
+
+SECTION "fixed", ROM0[$100]
+ds align[2] ; already aligned, 0 bytes
+db 8, 9, 10 ; three
+ds align[4, $e], 11 ; (1 << 4) - three - two = 11 bytes
+db 12, 13 ; two
+align 4
+assert @ - STARTOF("fixed") == 3 + 11 + 2
+
+SECTION "floating", ROM0
+db 14, 15 ; two
+ds align[4] ; not aligned, 0 bytes
+align 4 ; redundant
+db 16, 17, 18 ; three
+align 4, 3
+ds align[5], 19, 20 ; (1 << 4) - three = 13 bytes
+db 21 ; one
+align 5, 1
+assert @ - STARTOF("floating") == 2 + 3 + 13 + 1