[ruby/prism] Change pm_integer_t structure

https://github.com/ruby/prism/commit/588acf823f

6 files changed, 210 insertions, 206 deletions

diff --git a/prism/extension.c b/prism/extension.c
index 0115335855..1a471000b4 100644
--- a/prism/extension.c
+++ b/prism/extension.c
@@ -1047,12 +1047,16 @@ integer_parse(VALUE self, VALUE source) {
     pm_integer_t integer = { 0 };
     pm_integer_parse(&integer, PM_INTEGER_BASE_UNKNOWN, start, start + length);
 
-    VALUE number = UINT2NUM(integer.head.value);
-    size_t shift = 0;
+    VALUE number;
 
-    for (pm_integer_word_t *node = integer.head.next; node != NULL; node = node->next) {
-        VALUE receiver = rb_funcall(UINT2NUM(node->value), rb_intern("<<"), 1, ULONG2NUM(++shift * 32));
-        number = rb_funcall(receiver, rb_intern("|"), 1, number);
+    if (integer.values == NULL) {
+        number = UINT2NUM(integer.value);
+    } else {
+        number = UINT2NUM(0);
+        for (size_t i = 0; i < integer.length; i++) {
+            VALUE receiver = rb_funcall(UINT2NUM(integer.values[i]), rb_intern("<<"), 1, ULONG2NUM(i * 32));
+            number = rb_funcall(receiver, rb_intern("|"), 1, number);
+        }
     }
 
     if (integer.negative) number = rb_funcall(number, rb_intern("-@"), 0);
diff --git a/prism/static_literals.c b/prism/static_literals.c
index 713721bb73..81231692f6 100644
--- a/prism/static_literals.c
+++ b/prism/static_literals.c
@@ -53,12 +53,11 @@ node_hash(const pm_parser_t *parser, const pm_node_t *node) {
         case PM_INTEGER_NODE: {
             // Integers hash their value.
             const pm_integer_t *integer = &((const pm_integer_node_t *) node)->value;
-            const uint32_t *value = &integer->head.value;
-
-            uint32_t hash = murmur_hash((const uint8_t *) value, sizeof(uint32_t));
-            for (const pm_integer_word_t *word = integer->head.next; word != NULL; word = word->next) {
-                value = &word->value;
-                hash ^= murmur_hash((const uint8_t *) value, sizeof(uint32_t));
+            uint32_t hash;
+            if (integer->values) {
+                hash = murmur_hash((const uint8_t *) integer->values, sizeof(uint32_t) * integer->length);
+            } else {
+                hash = murmur_hash((const uint8_t *) &integer->value, sizeof(uint32_t));
             }
 
             if (integer->negative) {
@@ -204,9 +203,9 @@ pm_int64_value(const pm_parser_t *parser, const pm_node_t *node) {
     switch (PM_NODE_TYPE(node)) {
         case PM_INTEGER_NODE: {
             const pm_integer_t *integer = &((const pm_integer_node_t *) node)->value;
-            if (integer->length > 0) return integer->negative ? INT64_MIN : INT64_MAX;
+            if (integer->values) return integer->negative ? INT64_MIN : INT64_MAX;
 
-            int64_t value = (int64_t) integer->head.value;
+            int64_t value = (int64_t) integer->value;
             return integer->negative ? -value : value;
         }
         case PM_SOURCE_LINE_NODE:
diff --git a/prism/templates/ext/prism/api_node.c.erb b/prism/templates/ext/prism/api_node.c.erb
index 7b3e685a70..a195fa6325 100644
--- a/prism/templates/ext/prism/api_node.c.erb
+++ b/prism/templates/ext/prism/api_node.c.erb
@@ -40,20 +40,20 @@ pm_string_new(const pm_string_t *string, rb_encoding *encoding) {
 static VALUE
 pm_integer_new(const pm_integer_t *integer) {
     VALUE result;
-    if (integer->head.next) {
-        size_t length = integer->length + 1;
-        VALUE str = rb_str_new(NULL, length * 8);
+    if (integer->values) {
+        VALUE str = rb_str_new(NULL, integer->length * 8);
         unsigned char *buf = (unsigned char *)RSTRING_PTR(str);
-        size_t offset = length * 8;
-        for (const pm_integer_word_t *node = &integer->head; node != NULL; node = node->next) {
+        size_t offset = integer->length * 8;
+        for (size_t i = 0; i < integer->length; i++) {
+            uint32_t value = integer->values[i];
             for (int i = 0; i < 8; i++) {
-                int n = (node->value >> (4 * i)) & 0xf;
+                int n = (value >> (4 * i)) & 0xf;
                 buf[--offset] = n < 10 ? n + '0' : n - 10 + 'a';
             }
         }
         result = rb_funcall(str, rb_intern("to_i"), 1, UINT2NUM(16));
     } else {
-        result = UINT2NUM(integer->head.value);
+        result = UINT2NUM(integer->value);
     }
 
     if (integer->negative) {
diff --git a/prism/templates/src/serialize.c.erb b/prism/templates/src/serialize.c.erb
index 0313f43d78..27fde37f69 100644
--- a/prism/templates/src/serialize.c.erb
+++ b/prism/templates/src/serialize.c.erb
@@ -52,10 +52,14 @@ pm_serialize_string(const pm_parser_t *parser, const pm_string_t *string, pm_buf
 static void
 pm_serialize_integer(const pm_integer_t *integer, pm_buffer_t *buffer) {
     pm_buffer_append_byte(buffer, integer->negative ? 1 : 0);
-    pm_buffer_append_varuint(buffer, pm_sizet_to_u32(integer->length + 1));
-
-    for (const pm_integer_word_t *node = &integer->head; node != NULL; node = node->next) {
-        pm_buffer_append_varuint(buffer, node->value);
+    if (integer->values == NULL) {
+        pm_buffer_append_varuint(buffer, pm_sizet_to_u32(1));
+        pm_buffer_append_varuint(buffer, integer->value);
+    } else {
+        pm_buffer_append_varuint(buffer, pm_sizet_to_u32(integer->length));
+        for (size_t i = 0; i < integer->length; i++) {
+            pm_buffer_append_varuint(buffer, integer->values[i]);
+        }
     }
 }
 
diff --git a/prism/util/pm_integer.c b/prism/util/pm_integer.c
index 5bcb508c1c..4caedc4121 100644
--- a/prism/util/pm_integer.c
+++ b/prism/util/pm_integer.c
@@ -1,20 +1,14 @@
 #include "prism/util/pm_integer.h"
 
 /**
- * Bigint with arbitary base. In practice, base is 1<<32 or 10**9.
- * When base is 10**9, it acts as bigdecimal.
+ * Adds two positive pm_integer_t with the given base.
+ * Return pm_integer_t with values allocated. Not normalized.
  */
-typedef struct {
-    size_t length;
-    uint32_t *values;
-} bigint_t;
-
-/**
- * Adds two bigint_t with the given base.
- */
-static bigint_t
-big_add(bigint_t left, bigint_t right, uint64_t base) {
-    size_t length = (left.length < right.length ? right.length : left.length);
+static pm_integer_t
+big_add(pm_integer_t left_, pm_integer_t right_, uint64_t base) {
+    pm_integer_t left = left_.values ? left_ : (pm_integer_t) { 0, 1, &left_.value, false };
+    pm_integer_t right = right_.values ? right_ : (pm_integer_t) { 0, 1, &right_.value, false };
+    size_t length = left.length < right.length ? right.length : left.length;
     uint32_t *values = (uint32_t*) malloc(sizeof(uint32_t) * (length + 1));
     uint64_t carry = 0;
     for (size_t i = 0; i < length; i++) {
@@ -26,15 +20,19 @@ big_add(bigint_t left, bigint_t right, uint64_t base) {
         values[length] = (uint32_t) carry;
         length++;
     }
-    return (bigint_t) { length, values };
+    return (pm_integer_t) { 0, length, values, false };
 }
 
 /**
- * Calculates `a - b - c` with the given base.
- * Result is assumed to be positive value. Internal use for karatsuba_multiply.
+ * Internal use for karatsuba_multiply. Calculates `a - b - c` with the given
+ * base. Assume a, b, c, a - b - c all to be poitive.
+ * Return pm_integer_t with values allocated. Not normalized.
  */
-static bigint_t
-big_sub2(bigint_t a, bigint_t b, bigint_t c, uint64_t base) {
+static pm_integer_t
+big_sub2(pm_integer_t a_, pm_integer_t b_, pm_integer_t c_, uint64_t base) {
+    pm_integer_t a = a_.values ? a_ : (pm_integer_t) { 0, 1, &a_.value, false };
+    pm_integer_t b = b_.values ? b_ : (pm_integer_t) { 0, 1, &b_.value, false };
+    pm_integer_t c = c_.values ? c_ : (pm_integer_t) { 0, 1, &c_.value, false };
     size_t length = a.length;
     uint32_t *values = (uint32_t*) malloc(sizeof(uint32_t) * length);
     int64_t carry = 0;
@@ -50,16 +48,19 @@ big_sub2(bigint_t a, bigint_t b, bigint_t c, uint64_t base) {
         }
     }
     while (length > 1 && values[length - 1] == 0) length--;
-    return (bigint_t) { length, values };
+    return (pm_integer_t) { 0, length, values, false };
 }
 
 /**
- * Multiply two bigint_t with the given base using karatsuba algorithm.
+ * Multiply two positive integers with the given base using karatsuba algorithm.
+ * Return pm_integer_t with values allocated. Not normalized.
  */
-static bigint_t
-karatsuba_multiply(bigint_t left, bigint_t right, uint64_t base) {
+static pm_integer_t
+karatsuba_multiply(pm_integer_t left_, pm_integer_t right_, uint64_t base) {
+    pm_integer_t left = left_.values ? left_ : (pm_integer_t) { 0, 1, &left_.value, false };
+    pm_integer_t right = right_.values ? right_ : (pm_integer_t) { 0, 1, &right_.value, false };
     if (left.length > right.length) {
-        bigint_t temp = left;
+        pm_integer_t temp = left;
         left = right;
         right = temp;
     }
@@ -76,40 +77,40 @@ karatsuba_multiply(bigint_t left, bigint_t right, uint64_t base) {
             values[i + right.length] = carry;
         }
         while (length > 1 && values[length - 1] == 0) length--;
-        return (bigint_t) { length, values };
+        return (pm_integer_t) { 0, length, values, false };
     }
     if (left.length * 2 <= right.length) {
         uint32_t *values = (uint32_t*) calloc(left.length + right.length, sizeof(uint32_t));
         for (size_t start_offset = 0; start_offset < right.length; start_offset += left.length) {
             size_t end_offset = start_offset + left.length;
             if (end_offset > right.length) end_offset = right.length;
-            bigint_t sliced_right = { end_offset - start_offset, right.values + start_offset };
-            bigint_t v = karatsuba_multiply(left, sliced_right, base);
+            pm_integer_t sliced_right = { 0, end_offset - start_offset, right.values + start_offset, false };
+            pm_integer_t v = karatsuba_multiply(left, sliced_right, base);
             uint32_t carry = 0;
             for (size_t i = 0; i < v.length; i++) {
                 uint64_t sum = (uint64_t) values[start_offset + i] + v.values[i] + carry;
                 values[start_offset + i] = (uint32_t) (sum % base);
                 carry = (uint32_t) (sum / base);
             }
-            free(v.values);
-            values[start_offset + v.length] += carry;
+            if (carry > 0) values[start_offset + v.length] += carry;
+            pm_integer_free(&v);
         }
-        return (bigint_t) { left.length + right.length, values };
+        return (pm_integer_t) { 0, left.length + right.length, values, false };
     }
     size_t half = left.length / 2;
-    bigint_t x0 = { half, left.values };
-    bigint_t x1 = { left.length - half, left.values + half };
-    bigint_t y0 = { half, right.values };
-    bigint_t y1 = { right.length - half, right.values + half };
-    bigint_t z0 = karatsuba_multiply(x0, y0, base);
-    bigint_t z2 = karatsuba_multiply(x1, y1, base);
+    pm_integer_t x0 = { 0, half, left.values, false };
+    pm_integer_t x1 = { 0, left.length - half, left.values + half, false };
+    pm_integer_t y0 = { 0, half, right.values, false };
+    pm_integer_t y1 = { 0, right.length - half, right.values + half, false };
+    pm_integer_t z0 = karatsuba_multiply(x0, y0, base);
+    pm_integer_t z2 = karatsuba_multiply(x1, y1, base);
 
     // For simplicity to avoid considering negative values,
     // use `z1 = (x0 + x1) * (y0 + y1) - z0 - z2` instead of original karatsuba algorithm.
-    bigint_t x01 = big_add(x0, x1, base);
-    bigint_t y01 = big_add(y0, y1, base);
-    bigint_t xy = karatsuba_multiply(x01, y01, base);
-    bigint_t z1 = big_sub2(xy, z0, z2, base);
+    pm_integer_t x01 = big_add(x0, x1, base);
+    pm_integer_t y01 = big_add(y0, y1, base);
+    pm_integer_t xy = karatsuba_multiply(x01, y01, base);
+    pm_integer_t z1 = big_sub2(xy, z0, z2, base);
 
     size_t length = left.length + right.length;
     uint32_t *values = (uint32_t*) calloc(length, sizeof(uint32_t));
@@ -127,13 +128,13 @@ karatsuba_multiply(bigint_t left, bigint_t right, uint64_t base) {
         carry = (uint32_t) (sum / base);
     }
     while (length > 1 && values[length - 1] == 0) length--;
-    free(z0.values);
-    free(z1.values);
-    free(z2.values);
-    free(x01.values);
-    free(y01.values);
-    free(xy.values);
-    return (bigint_t) { length, values };
+    pm_integer_free(&z0);
+    pm_integer_free(&z1);
+    pm_integer_free(&z2);
+    pm_integer_free(&x01);
+    pm_integer_free(&y01);
+    pm_integer_free(&xy);
+    return (pm_integer_t) { 0, length, values, false };
 }
 
 /**
@@ -163,67 +164,95 @@ pm_integer_parse_digit(const uint8_t character) {
 }
 
 /**
- * Create a bigint_t from uint64_t with the given base.
+ * Create a pm_integer_t from uint64_t with the given base.
  */
-static bigint_t
-uint64_to_bigint(uint64_t value, uint64_t base) {
+static pm_integer_t
+pm_integer_from_uint64(uint64_t value, uint64_t base) {
+    if (value < base) {
+        return (pm_integer_t) { (uint32_t) value, 0, NULL, false };
+    }
     uint64_t v = value;
     size_t len = 0;
     while (value > 0) { len++; value /= base; }
-    if (len == 0) len = 1;
     uint32_t *values = (uint32_t*) malloc(sizeof(uint32_t) * len);
     for (size_t i = 0; i < len; i++) {
         values[i] = (uint32_t) (v % base);
         v /= base;
     }
-    return (bigint_t) { len, values };
+    return (pm_integer_t) { 0, len, values, false };
 }
 
 /**
- * Convert base of bigint.
+ * Normalize pm_integer_t.
+ * Heading zero values will be removed. If the integer fits into uint32_t,
+ * values is set to NULL, length is set to 0, and value field will be used.
+ */
+static void
+pm_integer_normalize(pm_integer_t *integer) {
+    if (integer->values == NULL) {
+        return;
+    }
+    while (integer->length > 1 && integer->values[integer->length - 1] == 0) {
+        integer->length--;
+    }
+    if (integer->length > 1) {
+        return;
+    }
+
+    uint32_t value = integer->values[0];
+    bool negative = integer->negative && value != 0;
+    pm_integer_free(integer);
+    *integer = (pm_integer_t) { value, 0, NULL, negative };
+}
+
+/**
+ * Convert base of the integer.
  * In practice, it converts 10**9 to 1<<32 or 1<<32 to 10**9.
  */
-static bigint_t
-karatsuba_convert_base(bigint_t source, uint64_t base_from, uint64_t base_to) {
+static pm_integer_t
+pm_integer_convert_base(pm_integer_t source_, uint64_t base_from, uint64_t base_to) {
+    pm_integer_t source = source_.values ? source_ : (pm_integer_t) { 0, 1, &source_.value, source_.negative };
     size_t bigints_length = (source.length + 1) / 2;
-    bigint_t *bigints = (bigint_t*) malloc(sizeof(bigint_t) * bigints_length);
+    pm_integer_t *bigints = (pm_integer_t*) malloc(sizeof(pm_integer_t) * bigints_length);
     for (size_t i = 0; i < source.length; i += 2) {
         uint64_t v = source.values[i] + base_from * (i + 1 < source.length ? source.values[i + 1] : 0);
-        bigints[i / 2] = uint64_to_bigint(v, base_to);
+        bigints[i / 2] = pm_integer_from_uint64(v, base_to);
     }
-    bigint_t base = uint64_to_bigint(base_from, base_to);
+    pm_integer_t base = pm_integer_from_uint64(base_from, base_to);
     while (bigints_length > 1) {
         size_t new_length = (bigints_length + 1) / 2;
-        bigint_t new_base = karatsuba_multiply(base, base, base_to);
-        free(base.values);
+        pm_integer_t new_base = karatsuba_multiply(base, base, base_to);
+        pm_integer_free(&base);
         base = new_base;
-        bigint_t *new_bigints = (bigint_t*) malloc(sizeof(bigint_t) * new_length);
+        pm_integer_t *new_bigints = (pm_integer_t*) malloc(sizeof(pm_integer_t) * new_length);
         for (size_t i = 0; i < bigints_length; i += 2) {
             if (i + 1 == bigints_length) {
                 new_bigints[i / 2] = bigints[i];
             } else {
-                bigint_t multiplied = karatsuba_multiply(base, bigints[i + 1], base_to);
+                pm_integer_t multiplied = karatsuba_multiply(base, bigints[i + 1], base_to);
                 new_bigints[i / 2] = big_add(bigints[i], multiplied, base_to);
-                free(bigints[i].values);
-                free(bigints[i + 1].values);
-                free(multiplied.values);
+                pm_integer_free(&bigints[i]);
+                pm_integer_free(&bigints[i + 1]);
+                pm_integer_free(&multiplied);
             }
         }
         free(bigints);
         bigints = new_bigints;
         bigints_length = new_length;
     }
-    free(base.values);
-    bigint_t result = bigints[0];
+    pm_integer_free(&base);
+    pm_integer_t result = bigints[0];
+    result.negative = source.negative;
     free(bigints);
+    pm_integer_normalize(&result);
     return result;
 }
 
 /**
- * Convert digits to bigint_t with the given power-of-two base.
+ * Convert digits to integer with the given power-of-two base.
  */
-static bigint_t
-big_parse_powof2(uint32_t base, const uint8_t *digits, size_t digits_length) {
+static void
+pm_integer_parse_powof2(pm_integer_t *integer, uint32_t base, const uint8_t *digits, size_t digits_length) {
     size_t bit = 1;
     while (base > (uint32_t) (1 << bit)) bit++;
     size_t length = (digits_length * bit + 31) / 32;
@@ -237,32 +266,31 @@ big_parse_powof2(uint32_t base, const uint8_t *digits, size_t digits_length) {
         if (32 - shift < bit) values[index + 1] |= value >> (32 - shift);
     }
     while (length > 1 && values[length - 1] == 0) length--;
-    return (bigint_t) { length, values };
+    *integer = (pm_integer_t) { 0, length, values, false };
+    pm_integer_normalize(integer);
 }
 
 /**
- * Convert decimal digits to bigint.
+ * Convert decimal digits to pm_integer_t.
  */
-static bigint_t
-big_parse_decimal(const uint8_t *digits, size_t digits_length) {
-    // Construct a bigdecimal from the digits.
+static void
+pm_integer_parse_decimal(pm_integer_t *integer, const uint8_t *digits, size_t digits_length) {
+    // Construct a bigdecimal with base = 10**9 from the digits
     const size_t batch = 9;
-    const uint64_t batch_base = 1000000000;
     size_t values_length = (digits_length + batch - 1) / batch;
-    bigint_t bigint = { values_length, (uint32_t*) calloc(values_length, sizeof(uint32_t)) };
+    pm_integer_t decimal = { 0, values_length, (uint32_t*) calloc(values_length, sizeof(uint32_t)), false };
     uint32_t v = 0;
     for (size_t i = 0; i < digits_length; i++) {
         v = v * 10 + digits[i];
         size_t reverse_index = digits_length - i - 1;
         if (reverse_index % batch == 0) {
-            bigint.values[reverse_index / batch] = v;
+            decimal.values[reverse_index / batch] = v;
             v = 0;
         }
     }
-    // Convert bigint base from 10**9 to 1<<32.
-    bigint_t converted = karatsuba_convert_base(bigint, batch_base, ((uint64_t) 1 << 32));
-    free(bigint.values);
-    return converted;
+    // Convert base from 10**9 to 1<<32.
+    *integer = pm_integer_convert_base(decimal, 1000000000, ((uint64_t) 1 << 32));
+    pm_integer_free(&decimal);
 }
 
 /**
@@ -277,22 +305,12 @@ pm_integer_parse_big(pm_integer_t *integer, uint32_t multiplier, const uint8_t *
         if (*start == '_') continue;
         digits[digits_length++] = (uint8_t) pm_integer_parse_digit(*start);
     }
-    // Construct bigint_t from the digits.
-    bigint_t bigint =
-        multiplier == 10 ? big_parse_decimal(digits, digits_length) : big_parse_powof2(multiplier, digits, digits_length);
-
-    // Pack bigint_t to pm_integer_t.
-    integer->length = bigint.length - 1;
-    integer->head.value = bigint.values[0];
-    pm_integer_word_t *current = &integer->head;
-    for (size_t i = 1; i < bigint.length; i++) {
-        current->next = malloc(sizeof(pm_integer_word_t));
-        current = current->next;
-        current->value = bigint.values[i];
-        current->next = NULL;
+    // Construct pm_integer_t from the digits.
+    if (multiplier == 10) {
+        pm_integer_parse_decimal(integer, digits, digits_length);
+    } else {
+        pm_integer_parse_powof2(integer, multiplier, digits, digits_length);
     }
-
-    free(bigint.values);
     free(digits);
 }
 
@@ -351,13 +369,13 @@ pm_integer_parse(pm_integer_t *integer, pm_integer_base_t base, const uint8_t *s
         if (*ptr == '_') continue;
         value = value * multiplier + pm_integer_parse_digit(*ptr);
         if (value > UINT32_MAX) {
-            // If the integer is too large to fit into a single node, then we'll
+            // If the integer is too large to fit into a single uint32_t, then we'll
             // parse it as a big integer.
             pm_integer_parse_big(integer, multiplier, start, end);
             return;
         }
     }
-    integer->head.value = (uint32_t) value;
+    integer->value = (uint32_t) value;
 }
 
 /**
@@ -365,7 +383,7 @@ pm_integer_parse(pm_integer_t *integer, pm_integer_base_t base, const uint8_t *s
  */
 size_t
 pm_integer_memsize(const pm_integer_t *integer) {
-    return sizeof(pm_integer_t) + integer->length * sizeof(pm_integer_word_t);
+    return sizeof(pm_integer_t) + integer->length * sizeof(uint32_t);
 }
 
 /**
@@ -378,16 +396,21 @@ pm_integer_compare(const pm_integer_t *left, const pm_integer_t *right) {
     if (left->negative != right->negative) return left->negative ? -1 : 1;
     int negative = left->negative ? -1 : 1;
 
-    if (left->length < right->length) return -1 * negative;
-    if (left->length > right->length) return 1 * negative;
+    if (left->values == right->values) {
+        if (left->value < right->value) return -1 * negative;
+        if (left->value > right->value) return 1 * negative;
+        return 0;
+    }
+
+    if (left->values == NULL || left->length < right->length) return -1 * negative;
+    if (right->values == NULL || left->length > right->length) return 1 * negative;
 
-    for (
-        const pm_integer_word_t *left_word = &left->head, *right_word = &right->head;
-        left_word != NULL && right_word != NULL;
-        left_word = left_word->next, right_word = right_word->next
-    ) {
-        if (left_word->value < right_word->value) return -1 * negative;
-        if (left_word->value > right_word->value) return 1 * negative;
+    for (size_t i = 0; i < left->length; i++) {
+        size_t index = left->length - i - 1;
+        uint32_t l = left->values[index];
+        uint32_t r = right->values[index];
+        if (l < r) return -1 * negative;
+        if (l > r) return 1 * negative;
     }
 
     return 0;
@@ -402,75 +425,54 @@ pm_integer_string(pm_buffer_t *buffer, const pm_integer_t *integer) {
         pm_buffer_append_byte(buffer, '-');
     }
 
-    switch (integer->length) {
-        case 0: {
-            const uint32_t value = integer->head.value;
-            pm_buffer_append_format(buffer, "%" PRIu32, value);
-            return;
-        }
-        case 1: {
-            const uint64_t value = ((uint64_t) integer->head.value) | (((uint64_t) integer->head.next->value) << 32);
-            pm_buffer_append_format(buffer, "%" PRIu64, value);
-            return;
-        }
-        default: {
-            // Pack pm_integer_t to bigint_t.
-            size_t length = integer->length + 1;
-            uint32_t *values = calloc(length, sizeof(uint32_t));
-            const pm_integer_word_t *current = &(integer->head);
-            for (size_t i = 0; i < length; i++) {
-                values[i] = current->value;
-                current = current->next;
-            }
-            bigint_t bigint = { length, values };
-            // Convert bigint base from 1<<32 to 10**9.
-            bigint_t converted = karatsuba_convert_base(bigint, (uint64_t) 1 << 32, 1000000000);
-            free(values);
-
-            // Allocate a buffer that we'll copy the decimal digits into.
-            size_t char_length = converted.length * 9;
-            char *digits = calloc(char_length, sizeof(char));
-            if (digits == NULL) return;
+    if (integer->values == NULL) {
+        pm_buffer_append_format(buffer, "%" PRIu32, integer->value);
+        return;
+    }
+    if (integer->length == 2) {
+        const uint64_t value = ((uint64_t) integer->values[0]) | ((uint64_t) integer->values[1] << 32);
+        pm_buffer_append_format(buffer, "%" PRIu64, value);
+        return;
+    }
 
-            // Pack bigdecimal to digits.
-            for (size_t i = 0; i < converted.length; i++) {
-                uint32_t v = converted.values[i];
-                for (size_t j = 0; j < 9; j++) {
-                    digits[char_length - 9 * i - j - 1] = (char) ('0' + v % 10);
-                    v /= 10;
-                }
-            }
-            size_t start_offset = 0;
-            while (start_offset < char_length - 1 && digits[start_offset] == '0') start_offset++;
+    // Convert base from 1<<32 to 10**9.
+    pm_integer_t converted = pm_integer_convert_base(*integer, (uint64_t) 1 << 32, 1000000000);
 
-            // Finally, append the string to the buffer and free the digits.
-            pm_buffer_append_string(buffer, digits + start_offset, char_length - start_offset);
-            free(digits);
-            free(converted.values);
-            return;
-        }
+    if (converted.values == NULL) {
+        pm_buffer_append_format(buffer, "%" PRIu32, converted.value);
+        pm_integer_free(&converted);
+        return;
     }
-}
 
-/**
- * Recursively destroy the linked list of an integer.
- */
-static void
-pm_integer_word_destroy(pm_integer_word_t *integer) {
-    if (integer->next != NULL) {
-        pm_integer_word_destroy(integer->next);
+    // Allocate a buffer that we'll copy the decimal digits into.
+    size_t char_length = converted.length * 9;
+    char *digits = calloc(char_length, sizeof(char));
+    if (digits == NULL) return;
+
+    // Pack bigdecimal to digits.
+    for (size_t i = 0; i < converted.length; i++) {
+        uint32_t v = converted.values[i];
+        for (size_t j = 0; j < 9; j++) {
+            digits[char_length - 9 * i - j - 1] = (char) ('0' + v % 10);
+            v /= 10;
+        }
     }
+    size_t start_offset = 0;
+    while (start_offset < char_length - 1 && digits[start_offset] == '0') start_offset++;
 
-    xfree(integer);
+    // Finally, append the string to the buffer and free the digits.
+    pm_buffer_append_string(buffer, digits + start_offset, char_length - start_offset);
+    free(digits);
+    pm_integer_free(&converted);
 }
 
 /**
  * Free the internal memory of an integer. This memory will only be allocated if
- * the integer exceeds the size of a single node in the linked list.
+ * the integer exceeds the size of a single uint32_t.
  */
 PRISM_EXPORTED_FUNCTION void
 pm_integer_free(pm_integer_t *integer) {
-    if (integer->head.next) {
-        pm_integer_word_destroy(integer->head.next);
+    if (integer->values) {
+        free(integer->values);
     }
 }
diff --git a/prism/util/pm_integer.h b/prism/util/pm_integer.h
index 63f560275d..7f172988b3 100644
--- a/prism/util/pm_integer.h
+++ b/prism/util/pm_integer.h
@@ -15,30 +15,25 @@
 #include <stdlib.h>
 
 /**
- * A node in the linked list of a pm_integer_t.
+ * A structure represents an arbitrary-sized integer.
  */
-typedef struct pm_integer_word {
-    /** A pointer to the next node in the list. */
-    struct pm_integer_word *next;
-
-    /** The value of the node. */
+typedef struct {
+    /**
+     * Embedded value for small integer. This value is set to 0 if the value
+     * does not fit into uint32_t.
+     */
     uint32_t value;
-} pm_integer_word_t;
 
-/**
- * This structure represents an arbitrary-sized integer. It is implemented as a
- * linked list of 32-bit integers, with the least significant digit at the head
- * of the list.
- */
-typedef struct {
-    /** The number of nodes in the linked list that have been allocated. */
+    /**
+     * The number of allocated values. length is set to 0 if the integer fits
+     * into uint32_t.
+     */
     size_t length;
 
     /**
-     * The head of the linked list, embedded directly so that allocations do not
-     * need to be performed for small integers.
+     * List of 32-bit integers. Set to NULL if the integer fits into uint32_t.
      */
-    pm_integer_word_t head;
+    uint32_t *values;
 
     /**
      * Whether or not the integer is negative. It is stored this way so that a