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Merged
dstelzer merged 2 commits into from
Sep 16, 2026
Merged

Improve locality of strings in WRIT chunk #357

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1b9b3c7
Group text strings by reference order for page locality
sehugg Sep 2, 2026
04019fc
updated readme
sehugg Sep 11, 2026
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5 changes: 5 additions & 0 deletions readme.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -48,6 +48,11 @@ Project website:

Release notes:

1c/04, Lib 1.2.4:

Compiler: Improved ordering of strings in WRIT chunk, which
improves performance on slow platforms like 6502.

1c/03, Lib 1.2.4:

Language: CSS text-decoration: reverse has been replaced with
Expand Down
74 changes: 57 additions & 17 deletions src/backend_aa.c
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Expand Up @@ -1277,7 +1277,7 @@ static void compile_routines(struct program *prg, struct predicate *pred, int fi
if(ci->subop == BOX_SPAN) {
ai = add_instr(AA_ENTER_SPAN);
ai->oper[0] = (aaoper_t) {AAO_INDEX, ci->oper[0].value};

if(prg->boxclasses[ci->oper[0].value].style & STYLE_INVISIBLE
&& !warned_about_invisible_spans) {
report(LVL_WARN, 0, "(span @%s) makes an invisible span. This is legal, but can produce strange spacing.", prg->boxclasses[ci->oper[0].value].class->name);
Expand Down Expand Up @@ -3175,14 +3175,36 @@ static int cmp_stringref(const void *a, const void *b) {
return (int) *aa - (int) *bb;
}

static int string_is_short(uint32_t addr) {
return addr <= 0xfe && !(addr & 1);
}

static int cmp_stringindex(const void *a, const void *b) {
return (int) *(const uint16_t *) a - (int) *(const uint16_t *) b;
}

// Lay the strings out in the given order. Strings in the one-byte operand
// range have to start at an even address.
static void place_strings(uint16_t *refs) {
uint32_t org = 0;
int i;

for(i = 0; i < n_textstr; i++) {
textstrings[refs[i]].address = org;
org += (textstrings[refs[i]].bitlength + 7) / 8;
if(org <= 253) {
org = (org + 1) & ~1;
}
}
writ_size = org;
}

static void analyze_strings() {
int i, j, n, dnum, len;
uint32_t bits;
uint8_t charcost[129];
uint8_t ch;
uint16_t refs[n_textstr];
struct textstring *ts;
uint32_t org;

for(i = 0; i < 129; i++) {
bits = charbits[i];
Expand Down Expand Up @@ -3215,19 +3237,37 @@ static void analyze_strings() {
refs[i] = i;
}

// Sort all strings by cost.
qsort(refs, n_textstr, sizeof(uint16_t), cmp_stringref);
// Initial string placement, deciding tiers and computing writ_size.
place_strings(refs);

org = 0;
for(i = 0; i < n_textstr; i++) {
ts = &textstrings[refs[i]];
ts->address = org;
//printf("%06x %4d %4d \"%s\"\n", org, (ts->bitlength + 7) / 8, ts->occurrences, ts->chars);
org += (ts->bitlength + 7) / 8;
if(org <= 253) {
org = (org + 1) & ~1;
// Now that we've decided the tiers, sort the medium and long tiers
// back into reference order to improve locality on antique backends.
for(n = 0; n < n_textstr; n++) {
if(!string_is_short(textstrings[refs[n]].address)) break;
}
for(i = n; i < n_textstr; i++) {
if(textstrings[refs[i]].address > 0x3fff) break;
}
qsort(refs + n, i - n, sizeof(uint16_t), cmp_stringindex);
qsort(refs + i, n_textstr - i, sizeof(uint16_t), cmp_stringindex);

if(i > n) {
// Move the longest string to the end, because it is the last
// string that starts below 0x4000 and crosses that boundary.
uint16_t longest;

for(j = n, len = n; j < i; j++) {
if(textstrings[refs[j]].bitlength > textstrings[refs[len]].bitlength) len = j;
}
longest = refs[len];
memmove(refs + len, refs + len + 1, (i - len - 1) * sizeof(uint16_t));
refs[i - 1] = longest;
}
writ_size = org;

// Final string placement.
place_strings(refs);
}

static int compile_endings_check(uint8_t *dest, int org, struct endings_point *pt) {
Expand Down Expand Up @@ -3577,7 +3617,7 @@ static void chunks_file(FILE *f, struct program *prg, char *resdir) {
if(pad) fputc(0, f);
free(buf);
free(pathbuf);

report(LVL_DEBUG, 0, "Added resource file %s (%d bytes)", prg->resources[i].stem, size);
}
}
Expand Down Expand Up @@ -3858,12 +3898,12 @@ static void chunk_look(FILE *f, struct program *prg, uint32_t *crc) {
for(bcl = prg->boxclasses[i].css_lines; bcl; bcl = bcl->next) {
org += strlen(bcl->data) + 1;
}

// Add space for the extra line
org += strlen(extraline);
org += strlen(prg->boxclasses[i].class->name);
org++;

org++;
}

Expand Down Expand Up @@ -3893,7 +3933,7 @@ static void chunk_look(FILE *f, struct program *prg, uint32_t *crc) {
putbyte_crc(prg->boxclasses[i].class->name[j], f, crc);
}
putbyte_crc(0, f, crc);

putbyte_crc(0, f, crc); // Terminator for the whole thing
}

Expand Down Expand Up @@ -4001,7 +4041,7 @@ void backend_aa(
fputc((crc >> 0) & 0xff, f);

fclose(f);

report(LVL_DEBUG, 0, "Objects used: %d of %d (%d%%)", prg->nworldobj, 0x1ffe, (prg->nworldobj)*100/0x1ffe);
report(LVL_DEBUG, 0, "Dictionary words used: %d of %d (%d%%)", prg->ndictword, 0x1dff, (prg->ndictword)*100/0x1dff);
report(LVL_DEBUG, 0, "Non-ASCII characters used: %d of %d (%d%%)", ncharmap, 128, ncharmap*100/128);
Expand Down
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