# Project Euler 808
# Reversible Prime Squares — sum of first 50 reversible prime squares.
extern {
function calloc(n: i64, size: i64) -> ptr<void>
function free(p: ptr<void>) -> void
}
function isqrt(n: i64) -> i64 {
if n < 2 { return n }
let mut x: i64 = n
let mut y: i64 = (x + 1) / 2
while y < x {
x = y
y = (x + n / x) / 2
}
return x
}
function reverse_num(x: i64) -> i64 {
let mut n: i64 = x
let mut r: i64 = 0
while n > 0 {
r = r * 10 + (n % 10)
n = n / 10
}
return r
}
function is_palindrome(x: i64) -> i32 {
if reverse_num(x) == x { return 1 }
return 0
}
function solve() -> i64 {
let limit: i64 = 50000000
let is_prime: ptr<i8> = calloc(limit + 1, 1)
# 0 = prime after sieve setup; mark composites as 1
is_prime[0] = 1
is_prime[1] = 1
let mut i: i64 = 2
while i * i <= limit {
if is_prime[i] == 0 {
let mut j: i64 = i * i
while j <= limit {
is_prime[j] = 1
j = j + i
}
}
i = i + 1
}
let values: ptr<i64> = calloc(200, 8)
let mut vcount: i64 = 0
let mut p: i64 = 11 # skip tiny primes; start past 2,3,5,7
while p <= limit {
if is_prime[p] == 0 {
let sq: i64 = p * p
if is_palindrome(sq) == 0 {
let rev: i64 = reverse_num(sq)
let r: i64 = isqrt(rev)
if r * r == rev && r <= limit && is_prime[r] == 0 {
# add both if unique
let mut found: i32 = 0
let mut k: i64 = 0
while k < vcount {
if values[k] == sq { found = 1 }
k = k + 1
}
if found == 0 {
values[vcount] = sq
vcount = vcount + 1
}
found = 0
k = 0
while k < vcount {
if values[k] == rev { found = 1 }
k = k + 1
}
if found == 0 {
values[vcount] = rev
vcount = vcount + 1
}
}
}
}
p = p + 1
}
# sort values
let mut a: i64 = 0
while a < vcount {
let mut b: i64 = a + 1
while b < vcount {
if values[b] < values[a] {
let t: i64 = values[a]
values[a] = values[b]
values[b] = t
}
b = b + 1
}
a = a + 1
}
let mut total: i64 = 0
let mut ntake: i64 = 50
if vcount < ntake { ntake = vcount }
a = 0
while a < ntake {
total = total + values[a]
a = a + 1
}
free(is_prime)
free(values)
return total
}
function main() -> i32 {
printf("%lld\n", solve())
return 0
}
Generated C
#include <stdint.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* Flow runtime helpers */
typedef struct flow_temp_node { struct flow_temp_node* next; } flow_temp_node;
static flow_temp_node* flow_temp_head = NULL;
static int flow_temp_atexit_set = 0;
__attribute__((unused)) static void flow_temp_free_all(void) {
while (flow_temp_head) {
flow_temp_node* n = flow_temp_head;
flow_temp_head = n->next;
free(n);
}
}
__attribute__((unused)) static void* flow_temp_alloc(size_t nbytes) {
flow_temp_node* node = (flow_temp_node*)malloc(sizeof(flow_temp_node) + nbytes);
if (!node) return NULL;
node->next = flow_temp_head;
flow_temp_head = node;
if (!flow_temp_atexit_set) {
flow_temp_atexit_set = 1;
atexit(flow_temp_free_all);
}
return (void*)(node + 1);
}
#ifndef FLOW_DIAG
#define FLOW_DIAG(msg) fprintf(stderr, "%s", (msg))
#endif
#ifndef FLOW_LOG
#define FLOW_LOG(fmt, ...) printf(fmt, __VA_ARGS__)
#endif
#ifndef FLOW_LOG_EMPTY
#define FLOW_LOG_EMPTY(fmt) printf(fmt)
#endif
static char* flow_strcat(const char* a, const char* b) {
size_t la = strlen(a ? a : ""), lb = strlen(b ? b : "");
char* r = (char*)flow_temp_alloc(la + lb + 1);
if (!r) return NULL;
if (la) memcpy(r, a, la);
if (lb) memcpy(r + la, b, lb);
r[la + lb] = '\0';
return r;
}
#define __flow_in_arr(arr, val) __extension__ ({ \
int _found = 0; \
size_t _n = sizeof(arr)/sizeof((arr)[0]); \
for (size_t _i = 0; _i < _n; _i++) { \
if ((arr)[_i] == (val)) { _found = 1; break; } \
} _found; })
/* Unified fault handler (MISRA #279) — override with -DFLOW_FAULT_HANDLER=fn */
#ifndef FLOW_FAULT_HANDLER
__attribute__((unused)) static inline void flow_fault_handler(const char* msg) {
fprintf(stderr, "flow: %s\n", msg ? msg : "fault");
abort();
#if defined(__GNUC__) || defined(__clang__)
__builtin_unreachable();
#endif
}
#else
#define flow_fault_handler FLOW_FAULT_HANDLER
#endif
#define flow_div_by_zero_handler() flow_fault_handler("division by zero")
#define flow_shift_ub_handler() flow_fault_handler("invalid shift (amount out of range or left-shift of negative)")
#ifndef FLOW_CHECKED_DIV
#define FLOW_CHECKED_DIV(L, R) (((R) != 0) ? ((L) / (R)) : (flow_div_by_zero_handler(), (L) * 0))
#endif
#ifndef FLOW_CHECKED_MOD
#define FLOW_CHECKED_MOD(L, R) (((R) != 0) ? ((L) % (R)) : (flow_div_by_zero_handler(), (L) * 0))
#endif
#ifndef FLOW_CHECKED_SHL
#define FLOW_CHECKED_SHL(L, R) ((((R) >= 0) && ((unsigned long long)(R) < (sizeof(L) * 8ull)) && ((L) >= 0)) ? ((L) << (R)) : (flow_shift_ub_handler(), (L) * 0))
#endif
#ifndef FLOW_CHECKED_SHR
#define FLOW_CHECKED_SHR(L, R) ((((R) >= 0) && ((unsigned long long)(R) < (sizeof(L) * 8ull))) ? ((L) >> (R)) : (flow_shift_ub_handler(), (L) * 0))
#endif
#include <math.h>
void* _ui_state = NULL;
static inline float i32_to_f32(int32_t v) { return (float)v; }
/* Host stub for @gpu kernels (device codegen replaces this). */
static inline int32_t gpu_thread_id(void) { return 0; }
int64_t isqrt_i64(int64_t n);
int64_t reverse_num_i64(int64_t x);
int32_t is_palindrome_i64(int64_t x);
int64_t solve(void);
int32_t main(void);
int64_t isqrt_i64(int64_t n) {
if (n < 2) {
return n;
}
int64_t x = n;
int64_t y = FLOW_CHECKED_DIV(((x + 1)), (2));
while (y < x) {
x = y;
y = FLOW_CHECKED_DIV(((x + FLOW_CHECKED_DIV((n), (x)))), (2));
}
return x;
}
int64_t reverse_num_i64(int64_t x) {
int64_t n = x;
int64_t r = 0;
while (n > 0) {
r = ((r * 10) + FLOW_CHECKED_MOD((n), (10)));
n = FLOW_CHECKED_DIV((n), (10));
}
return r;
}
int32_t is_palindrome_i64(int64_t x) {
if (reverse_num_i64(x) == x) {
return 1;
}
return 0;
}
int64_t solve(void) {
int64_t limit = 50000000;
int8_t* is_prime = (int8_t*)(calloc((limit + 1), 1));
is_prime[0] = 1;
is_prime[1] = 1;
int64_t i = 2;
while ((i * i) <= limit) {
if (is_prime[i] == 0) {
int64_t j = (i * i);
while (j <= limit) {
is_prime[j] = 1;
j = (j + i);
}
}
i = (i + 1);
}
int64_t* values = (int64_t*)(calloc(200, 8));
int64_t vcount = 0;
int64_t p = 11;
while (p <= limit) {
if (is_prime[p] == 0) {
int64_t sq = (p * p);
if (is_palindrome_i64(sq) == 0) {
int64_t rev = reverse_num_i64(sq);
int64_t r = isqrt_i64(rev);
if ((((r * r) == rev && r <= limit) && is_prime[r] == 0)) {
int32_t found = 0;
int64_t k = 0;
while (k < vcount) {
if (values[k] == sq) {
found = 1;
}
k = (k + 1);
}
if (found == 0) {
values[vcount] = sq;
vcount = (vcount + 1);
}
found = 0;
k = 0;
while (k < vcount) {
if (values[k] == rev) {
found = 1;
}
k = (k + 1);
}
if (found == 0) {
values[vcount] = rev;
vcount = (vcount + 1);
}
}
}
}
p = (p + 1);
}
int64_t a = 0;
while (a < vcount) {
int64_t b = (a + 1);
while (b < vcount) {
if (values[b] < values[a]) {
int64_t t = values[a];
values[a] = values[b];
values[b] = t;
}
b = (b + 1);
}
a = (a + 1);
}
int64_t total = 0;
int64_t ntake = 50;
if (vcount < ntake) {
ntake = vcount;
}
a = 0;
while (a < ntake) {
total = (total + values[a]);
a = (a + 1);
}
free(is_prime);
free(values);
return total;
}
int32_t main(void) {
printf("%lld\n", solve());
return 0;
}