Skip to content

binary search the dispatch lookup when ranges are irregular #35

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
dougchansan wants to merge 1 commit into
base: main
Choose a base branch
from
+143 −0
Open

binary search the dispatch lookup when ranges are irregular #35

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
79 changes: 79 additions & 0 deletions src/backend/dispatch.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -306,12 +306,91 @@ static int emit_lookup_indexed(FILE* out, const FunctionList* funcs) {
return 1;
}

// Past a few uniform runs, binary search beats a linear chain of range checks.
#define DISPATCH_LINEAR_MAX_RUNS 16u

static int emit_lookup_search(FILE* out, const FunctionList* funcs,
const char* symbol_suffix) {
FunctionRange* sorted =
(FunctionRange*)malloc(funcs->count * sizeof(*sorted));
if (!sorted)
return 0;
u32 count = 0;
for (u32 i = 0; i < funcs->count; i++) {
if (funcs->ranges[i].start < funcs->ranges[i].end)
sorted[count++] = funcs->ranges[i];
}
if (count == 0) {
free(sorted);
return 0;
}
qsort(sorted, count, sizeof(*sorted), range_compare);
// Overlapping ranges keep the linear form to preserve first-match order.
for (u32 i = 1; i < count; i++) {
if (sorted[i - 1u].end > sorted[i].start) {
free(sorted);
return 0;
}
}

// Coverage guard; module-table generators scrape this form.
fprintf(out, " if (!(");
for (u32 i = 0; i < count;) {
u32 span_end = i + 1u;
while (span_end < count && sorted[span_end - 1u].end == sorted[span_end].start)
span_end++;
fprintf(out, "%s\n (address >= 0x%08Xu && address < 0x%08Xu)",
i ? " ||" : "", sorted[i].start, sorted[span_end - 1u].end);
i = span_end;
}
fprintf(out, "))\n return NULL;\n");
fprintf(out, " static const u32 range_start[%u] = {\n", count);
for (u32 i = 0; i < count; i++)
fprintf(out, " 0x%08Xu,\n", sorted[i].start);
fprintf(out, " };\n");
fprintf(out, " static const u32 range_end[%u] = {\n", count);
for (u32 i = 0; i < count; i++)
fprintf(out, " 0x%08Xu,\n", sorted[i].end);
fprintf(out, " };\n");
fprintf(out, " static const DolRecompFunction range_function[%u] = {\n",
count);
for (u32 i = 0; i < count; i++)
fprintf(out, " func_%08X%s,\n", sorted[i].start, symbol_suffix);
fprintf(out, " };\n");
fprintf(out, " u32 low = 0u;\n");
fprintf(out, " u32 high = %uu;\n", count);
fprintf(out, " while (low < high) {\n");
fprintf(out, " u32 middle = low + ((high - low) >> 1);\n");
fprintf(out, " if (range_start[middle] <= address)\n");
fprintf(out, " low = middle + 1u;\n");
fprintf(out, " else\n");
fprintf(out, " high = middle;\n");
fprintf(out, " }\n");
fprintf(out, " if (low == 0u)\n");
fprintf(out, " return NULL;\n");
fprintf(out, " low--;\n");
fprintf(out,
" if (address < range_end[low] && "
"((address - range_start[low]) & 3u) == 0u)\n");
fprintf(out, " return range_function[low];\n");
fprintf(out, " return NULL;\n");
fprintf(out, "}\n");
free(sorted);
return 1;
}

void emit_function_lookup(FILE* out, const FunctionList* funcs,
const char* symbol_suffix) {
fprintf(out,
"\nstatic inline DolRecompFunction "
"dolrecomp_find_original%s(u32 address) {\n",
symbol_suffix);
u32 run_count = 0;
for (u32 first = 0; first < funcs->count; run_count++)
first = uniform_run_end(funcs, first);
if (run_count > DISPATCH_LINEAR_MAX_RUNS &&
emit_lookup_search(out, funcs, symbol_suffix))
return;
for (u32 first = 0; first < funcs->count;) {
u32 end = uniform_run_end(funcs, first);
emit_lookup_run(out, funcs, first, end, symbol_suffix);
Expand Down
64 changes: 64 additions & 0 deletions tests/test_dispatch.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -81,7 +81,71 @@ static char* emit_dispatch_to_string(void) {
return buf;
}

// Many irregular ranges in two gapped spans, as function partitioning emits.
static char* emit_irregular_lookup_to_string(void) {
FunctionList funcs = {0};
FILE* f = NULL;
char* buf = NULL;
u32 start = BASE;

for (u32 i = 0; i < 40u; i++) {
u32 width = 0x10u + (i % 5u) * 0x8u;
if (i == 20u)
start = BASE + 0x2000u;
if (!function_list_add(&funcs, start, start + width)) {
function_list_free(&funcs);
return NULL;
}
start += width;
}

f = tmpfile();
if (!f) {
function_list_free(&funcs);
return NULL;
}
emit_function_lookup(f, &funcs, "");
function_list_free(&funcs);
fflush(f);

long size = ftell(f);
if (size < 0) {
fclose(f);
return NULL;
}
rewind(f);
buf = (char*)malloc((size_t)size + 1u);
if (!buf) {
fclose(f);
return NULL;
}
size_t got = fread(buf, 1, (size_t)size, f);
buf[got] = '\0';
fclose(f);
return buf;
}

int main(void) {
char* irregular = emit_irregular_lookup_to_string();
if (!irregular) {
check(0, "irregular: emit lookup");
} else {
check(strstr(irregular, "static const u32 range_start[40]") != NULL &&
strstr(irregular, "static const DolRecompFunction range_function[40]") != NULL &&
strstr(irregular, "if (range_start[middle] <= address)") != NULL,
"irregular: many ranges use a sorted search");
check(strstr(irregular, "return func_") == NULL &&
strstr(irregular, "chunk_functions") == NULL,
"irregular: no linear range-test chain remains");
check(strstr(irregular, "(address >= 0x80003000u && address < 0x80003280u)") != NULL &&
strstr(irregular, "(address >= 0x80005000u && address < 0x80005280u)") != NULL,
"irregular: coverage guard lists each contiguous span");
check(strstr(irregular, "func_80003000,") != NULL &&
strstr(irregular, "func_80005000,") != NULL,
"irregular: table covers both spans");
free(irregular);
}

char* code = emit_dispatch_to_string();
if (!code) {
check(0, "emit dispatch helpers");
Expand Down
Loading