utils: add int*_write_to_ascii_buf functions

Add functions for converting integers to a string, that are better
suited for our usage.

These new functions they likely perform better than lltoa, since they
don't rely on helpers for 64 bit division, and also compiler
optimization friendly functions for base 10 and 16 are provided:
Compiler is able to optimize n / k, when k is a known constant, by
replacing it with a multiplication.

Note that these new functions will write characters without C string
terminator.

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

Author: bettio

src/libAtomVM/CMakeLists.txt

@@ -102,6 +102,7 @@ set(SOURCE_FILES
     term.c
     timer_list.c
     unicode.c
+    utils.c
     valueshashtable.c
 )
 

src/libAtomVM/utils.c

@@ -0,0 +1,192 @@
+/*
+ * This file is part of AtomVM.
+ *
+ * Copyright 2025 Davide Bettio <davide@uninstall.it>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later
+ */
+
+#include "utils.h"
+
+#include <inttypes.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+
+static char *uintptr_to_a_n(uintptr_t n, unsigned int base, char *out_end)
+{
+    ASSUME((base >= 2) && (base <= 36));
+
+    char *c = out_end;
+    uintptr_t q = n;
+    do {
+        c--;
+        uintptr_t r = (q % base);
+        *c = (r <= 9) ? '0' + r : 'A' + r - 10;
+        q /= base;
+    } while (q);
+
+    return c;
+}
+
+static char *uintptr_to_a_10(uintptr_t n, char *out_end)
+{
+    char *c = out_end;
+    uintptr_t q = n;
+    do {
+        c--;
+        *c = '0' + (q % 10);
+        q /= 10;
+    } while (q);
+
+    return c;
+}
+
+static char *uintptr_to_a_16(uintptr_t n, char *out_end)
+{
+    char *c = out_end;
+    uintptr_t q = n;
+    do {
+        c--;
+        uintptr_t r = (q & 0xF);
+        *c = (r <= 9) ? '0' + r : 'A' + r - 10;
+        q >>= 4;
+    } while (q);
+
+    return c;
+}
+
+size_t intptr_write_to_ascii_buf(intptr_t n, unsigned int base, char *out_end)
+{
+    ASSUME((base >= 2) && (base <= 36));
+
+    // let's avoid undefined behaviors
+    // -INTPTR_MIN is INTPTR_MAX + 1
+    uintptr_t pos_n;
+    if (n >= 0) {
+        pos_n = n;
+    } else if (n == INTPTR_MIN) {
+        pos_n = ((uintptr_t) INTPTR_MAX) + 1;
+    } else {
+        pos_n = -n;
+    }
+
+    char *c;
+
+    // use optimized versions for 10 and 16
+    switch (base) {
+        case 10:
+            c = uintptr_to_a_10(pos_n, out_end);
+            break;
+        case 16:
+            c = uintptr_to_a_16(pos_n, out_end);
+            break;
+        default:
+            c = uintptr_to_a_n(pos_n, base, out_end);
+            break;
+    }
+
+    if (n < 0) {
+        c--;
+        *c = '-';
+    }
+
+    return out_end - c;
+}
+
+#if INT64_MAX > INTPTR_MAX
+
+static char *uint64_to_a_n(uint64_t n, unsigned int base, char *out_end)
+{
+    ASSUME((base >= 2) && (base <= 36));
+
+    char *c = out_end;
+    uint64_t q = n;
+    do {
+        c--;
+        uint64_t r = (q % base);
+        *c = (r <= 9) ? '0' + r : 'A' + r - 10;
+        q /= base;
+    } while (q);
+
+    return c;
+}
+
+static char *uint64_to_a_10(uint64_t n, char *out_end)
+{
+    char *c = out_end;
+    uint64_t q = n;
+    do {
+        c--;
+        *c = '0' + (q % 10);
+        q /= 10;
+    } while (q);
+
+    return c;
+}
+
+static char *uint64_to_a_16(uint64_t n, char *out_end)
+{
+    char *c = out_end;
+    uint64_t q = n;
+    do {
+        c--;
+        uint64_t r = (q & 0xF);
+        *c = (r <= 9) ? '0' + r : 'A' + r - 10;
+        q >>= 4;
+    } while (q);
+
+    return c;
+}
+
+size_t int64_write_to_ascii_buf(int64_t n, unsigned int base, char *out_end)
+{
+    ASSUME((base >= 2) && (base <= 36));
+
+    // let's avoid undefined behaviors
+    // -INT64_MIN is INT64_MAX + 1
+    uint64_t pos_n;
+    if (n >= 0) {
+        pos_n = n;
+    } else if (n == INT64_MIN) {
+        pos_n = ((uint64_t) INT64_MAX) + 1;
+    } else {
+        pos_n = -n;
+    }
+
+    char *c;
+
+    // use optimized versions for 10 and 16
+    switch (base) {
+        case 10:
+            c = uint64_to_a_10(pos_n, out_end);
+            break;
+        case 16:
+            c = uint64_to_a_16(pos_n, out_end);
+            break;
+        default:
+            c = uint64_to_a_n(pos_n, base, out_end);
+            break;
+    }
+
+    if (n < 0) {
+        c--;
+        *c = '-';
+    }
+
+    return out_end - c;
+}
+
+#endif

src/libAtomVM/utils.h

@@ -28,6 +28,7 @@
 #ifndef _UTILS_H_
 #define _UTILS_H_
 
+#include <inttypes.h>
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -347,6 +348,33 @@ static inline __attribute__((always_inline)) func_ptr_t cast_void_to_func_ptr(vo
 #define ASSUME(...)
 #endif
 
+#if INTPTR_MAX <= INT32_MAX
+#define INTPTR_WRITE_TO_ASCII_BUF_LEN (32 + 1)
+#elif INTPTR_MAX <= INT64_MAX
+#define INTPTR_WRITE_TO_ASCII_BUF_LEN (64 + 1)
+#endif
+
+#define INT32_WRITE_TO_ASCII_BUF_LEN (32 + 1)
+#define INT64_WRITE_TO_ASCII_BUF_LEN (64 + 1)
+
+size_t intptr_write_to_ascii_buf(intptr_t n, unsigned int base, char *out_end);
+
+#if INTPTR_MAX >= INT32_MAX
+static inline size_t int32_write_to_ascii_buf(int32_t n, unsigned int base, char *out_end)
+{
+    return intptr_write_to_ascii_buf(n, base, out_end);
+}
+#endif
+
+#if INT64_MAX > INTPTR_MAX
+size_t int64_write_to_ascii_buf(int64_t n, unsigned int base, char *out_end);
+#else
+static inline size_t int64_write_to_ascii_buf(int64_t n, unsigned int base, char *out_end)
+{
+    return intptr_write_to_ascii_buf(n, base, out_end);
+}
+#endif
+
 #ifdef __cplusplus
 }
 #endif