Add new term_initialize_bigint function

Use `term_initialize_bigint` instead of `term_intn_data` + `intn_copy`

Signed-off-by: Davide Bettio <davide@uninstall.it>

Author: bettio

src/libAtomVM/bif.c

@@ -819,8 +819,7 @@ static term make_bigint(Context *ctx, uint32_t fail_label, uint32_t live,
 
         term bigres_term = term_create_uninitialized_intn(
             intn_data_size, (term_integer_sign_t) sign, &ctx->heap);
-        intn_digit_t *dest_buf = (void *) term_intn_data(bigres_term);
-        intn_copy(bigres, count, dest_buf, rounded_res_len);
+        term_initialize_bigint(bigres_term, bigres, count, rounded_res_len);
 
         return bigres_term;
     } else {

src/libAtomVM/externalterm.c

@@ -597,8 +597,7 @@ static term parse_external_terms(const uint8_t *external_term_buf, size_t *eterm
             intn_integer_sign_t sign = is_negative ? IntNNegativeInteger : IntNPositiveInteger;
             term bigint_term
                 = term_create_uninitialized_intn(intn_data_size, (term_integer_sign_t) sign, heap);
-            intn_digit_t *dest_buf = (void *) term_intn_data(bigint_term);
-            intn_copy(bigint, count, dest_buf, rounded_res_len);
+            term_initialize_bigint(bigint_term, bigint, count, rounded_res_len);
 
             return bigint_term;
         }

src/libAtomVM/jit.c

@@ -637,7 +637,9 @@ static term jit_alloc_big_integer_fragment(
 
     term bigint_term
         = term_create_uninitialized_intn(intn_data_size, (term_integer_sign_t) sign, &heap);
-    void *digits_mem = term_intn_data(bigint_term);
+    // Assumption: here we assume that bigints have standard boxed term layout
+    // This code might need to be updated when changing bigint memory layout
+    void *digits_mem = (void *) (term_to_const_term_ptr(bigint_term) + 1);
     // TODO: optimize: just initialize space that will not be used
     memset(digits_mem, 0, intn_data_size * sizeof(term));
 

src/libAtomVM/nifs.c

@@ -2065,8 +2065,7 @@ static term make_bigint(Context *ctx, const intn_digit_t bigres[], size_t bigres
 
     term bigres_term
         = term_create_uninitialized_intn(intn_data_size, (term_integer_sign_t) sign, &ctx->heap);
-    intn_digit_t *dest_buf = (void *) term_intn_data(bigres_term);
-    intn_copy(bigres, bigres_len, dest_buf, rounded_res_len);
+    term_initialize_bigint(bigres_term, bigres, bigres_len, rounded_res_len);
 
     return bigres_term;
 }

src/libAtomVM/opcodesswitch.h

@@ -1853,8 +1853,7 @@ static bool maybe_call_native(Context *ctx, atom_index_t module_name, atom_index
 
             term bigint_term
                 = term_create_uninitialized_intn(intn_data_size, (term_integer_sign_t) sign, &heap);
-            intn_digit_t *dest_buf = (void *) term_intn_data(bigint_term);
-            intn_copy(bigint, count, dest_buf, rounded_res_len);
+            term_initialize_bigint(bigint_term, bigint, count, rounded_res_len);
 
             memory_heap_append_heap(&ctx->heap, &heap);
 

src/libAtomVM/term.h

@@ -1309,10 +1309,37 @@ static inline term term_create_uninitialized_intn(size_t n, term_integer_sign_t
     return ((term) boxed_int) | TERM_PRIMARY_BOXED;
 }
 
-static inline void *term_intn_data(term t)
+/**
+ * @brief Initialize multi-precision integer data in a pre-allocated term
+ *
+ * Copies multi-precision integer digits into an already allocated boxed term,
+ * zero-extending to fill the entire allocated space. This function is used
+ * after creating an uninitialized bigint term to populate it with actual data.
+ *
+ * @param t Uninitialized bigint term (created with \c term_create_uninitialized_intn())
+ * @param bigint Source digit array to copy
+ * @param bigint_len Number of digits in source array
+ * @param uninitialized_size Total size of destination buffer in digits
+ *
+ * @pre t must be a valid uninitialized bigint term
+ * @pre bigint != NULL
+ * @pre uninitialized_size must match the size allocated for the term
+ *
+ * @post Copies bigint_len digits from source to term
+ * @post Zero-fills remaining space from bigint_len to uninitialized_size
+ *
+ * @note This function does not set the sign - that should be done when creating the term
+ * @note The destination buffer size (uninitialized_size) is typically rounded up for alignment
+ *
+ * @see term_create_uninitialized_intn() to allocate the term before initialization
+ * @see intn_copy() which performs the actual copy and zero-extension
+ */
+static inline void term_initialize_bigint(
+    term t, const intn_digit_t *bigint, size_t bigint_len, size_t uninitialized_size)
 {
     const term *boxed_value = term_to_const_term_ptr(t);
-    return (void *) (boxed_value + 1);
+    intn_digit_t *dest_buf = (intn_digit_t *) (boxed_value + 1);
+    intn_copy(bigint, bigint_len, dest_buf, uninitialized_size);
 }
 
 static inline void term_intn_to_term_size(size_t n, size_t *intn_data_size, size_t *rounded_num_len)
@@ -1404,9 +1431,9 @@ _Static_assert(
 static inline void term_to_bigint(
     term t, const intn_digit_t *bigint[], size_t *bigint_len, intn_integer_sign_t *bigint_sign)
 {
-    *bigint = (const intn_digit_t *) term_intn_data(t);
-
     const term *boxed_value = term_to_const_term_ptr(t);
+    *bigint = (const intn_digit_t *) (boxed_value + 1);
+
     size_t boxed_size = term_get_size_from_boxed_header(boxed_value[0]);
     *bigint_len = boxed_size * (sizeof(term) / sizeof(intn_digit_t));