util.h

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/***********************************************************************
 * Copyright (c) 2013, 2014 Pieter Wuille                              *
 * Distributed under the MIT software license, see the accompanying    *
 * file COPYING or https://www.opensource.org/licenses/mit-license.php.*
 ***********************************************************************/

#ifndef SECP256K1_UTIL_H
#define SECP256K1_UTIL_H

#if defined HAVE_CONFIG_H
#include "libsecp256k1-config.h"
#endif

#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <limits.h>

typedef struct {
    void (*fn)(const char *text, void* data);
    const void* data;
} secp256k1_callback;

static SECP256K1_INLINE void secp256k1_callback_call(const secp256k1_callback * const cb, const char * const text) {
    cb->fn(text, (void*)cb->data);
}

#ifdef DETERMINISTIC
#define TEST_FAILURE(msg) do { \
    fprintf(stderr, "%s\n", msg); \
    abort(); \
} while(0);
#else
#define TEST_FAILURE(msg) do { \
    fprintf(stderr, "%s:%d: %s\n", __FILE__, __LINE__, msg); \
    abort(); \
} while(0)
#endif

#if SECP256K1_GNUC_PREREQ(3, 0)
#define EXPECT(x,c) __builtin_expect((x),(c))
#else
#define EXPECT(x,c) (x)
#endif

#ifdef DETERMINISTIC
#define CHECK(cond) do { \
    if (EXPECT(!(cond), 0)) { \
        TEST_FAILURE("test condition failed"); \
    } \
} while(0)
#else
#define CHECK(cond) do { \
    if (EXPECT(!(cond), 0)) { \
        TEST_FAILURE("test condition failed: " #cond); \
    } \
} while(0)
#endif

/* Like assert(), but when VERIFY is defined, and side-effect safe. */
#if defined(COVERAGE)
#define VERIFY_CHECK(check)
#define VERIFY_SETUP(stmt)
#elif defined(VERIFY)
#define VERIFY_CHECK CHECK
#define VERIFY_SETUP(stmt) do { stmt; } while(0)
#else
#define VERIFY_CHECK(cond) do { (void)(cond); } while(0)
#define VERIFY_SETUP(stmt)
#endif

/* Define `VG_UNDEF` and `VG_CHECK` when VALGRIND is defined  */
#if !defined(VG_CHECK)
# if defined(VALGRIND)
#  include <valgrind/memcheck.h>
#  define VG_UNDEF(x,y) VALGRIND_MAKE_MEM_UNDEFINED((x),(y))
#  define VG_CHECK(x,y) VALGRIND_CHECK_MEM_IS_DEFINED((x),(y))
# else
#  define VG_UNDEF(x,y)
#  define VG_CHECK(x,y)
# endif
#endif

/* Like `VG_CHECK` but on VERIFY only */
#if defined(VERIFY)
#define VG_CHECK_VERIFY(x,y) VG_CHECK((x), (y))
#else
#define VG_CHECK_VERIFY(x,y)
#endif

static SECP256K1_INLINE void *checked_malloc(const secp256k1_callback* cb, size_t size) {
    void *ret = malloc(size);
    if (ret == NULL) {
        secp256k1_callback_call(cb, "Out of memory");
    }
    return ret;
}

static SECP256K1_INLINE void *checked_realloc(const secp256k1_callback* cb, void *ptr, size_t size) {
    void *ret = realloc(ptr, size);
    if (ret == NULL) {
        secp256k1_callback_call(cb, "Out of memory");
    }
    return ret;
}

#if defined(__BIGGEST_ALIGNMENT__)
#define ALIGNMENT __BIGGEST_ALIGNMENT__
#else
/* Using 16 bytes alignment because common architectures never have alignment
 * requirements above 8 for any of the types we care about. In addition we
 * leave some room because currently we don't care about a few bytes. */
#define ALIGNMENT 16
#endif

#define ROUND_TO_ALIGN(size) ((((size) + ALIGNMENT - 1) / ALIGNMENT) * ALIGNMENT)

/* Assume there is a contiguous memory object with bounds [base, base + max_size)
 * of which the memory range [base, *prealloc_ptr) is already allocated for usage,
 * where *prealloc_ptr is an aligned pointer. In that setting, this functions
 * reserves the subobject [*prealloc_ptr, *prealloc_ptr + alloc_size) of
 * alloc_size bytes by increasing *prealloc_ptr accordingly, taking into account
 * alignment requirements.
 *
 * The function returns an aligned pointer to the newly allocated subobject.
 *
 * This is useful for manual memory management: if we're simply given a block
 * [base, base + max_size), the caller can use this function to allocate memory
 * in this block and keep track of the current allocation state with *prealloc_ptr.
 *
 * It is VERIFY_CHECKed that there is enough space left in the memory object and
 * *prealloc_ptr is aligned relative to base.
 */
static SECP256K1_INLINE void *manual_alloc(void** prealloc_ptr, size_t alloc_size, void* base, size_t max_size) {
    size_t aligned_alloc_size = ROUND_TO_ALIGN(alloc_size);
    void* ret;
    VERIFY_CHECK(prealloc_ptr != NULL);
    VERIFY_CHECK(*prealloc_ptr != NULL);
    VERIFY_CHECK(base != NULL);
    VERIFY_CHECK((unsigned char*)*prealloc_ptr >= (unsigned char*)base);
    VERIFY_CHECK(((unsigned char*)*prealloc_ptr - (unsigned char*)base) % ALIGNMENT == 0);
    VERIFY_CHECK((unsigned char*)*prealloc_ptr - (unsigned char*)base + aligned_alloc_size <= max_size);
    ret = *prealloc_ptr;
    *prealloc_ptr = (unsigned char*)*prealloc_ptr + aligned_alloc_size;
    return ret;
}

/* Macro for restrict, when available and not in a VERIFY build. */
#if defined(SECP256K1_BUILD) && defined(VERIFY)
# define SECP256K1_RESTRICT
#else
# if (!defined(__STDC_VERSION__) || (__STDC_VERSION__ < 199901L) )
#  if SECP256K1_GNUC_PREREQ(3,0)
#   define SECP256K1_RESTRICT __restrict__
#  elif (defined(_MSC_VER) && _MSC_VER >= 1400)
#   define SECP256K1_RESTRICT __restrict
#  else
#   define SECP256K1_RESTRICT
#  endif
# else
#  define SECP256K1_RESTRICT restrict
# endif
#endif

#if defined(_WIN32)
# define I64FORMAT "I64d"
# define I64uFORMAT "I64u"
#else
# define I64FORMAT "lld"
# define I64uFORMAT "llu"
#endif

#if defined(__GNUC__)
# define SECP256K1_GNUC_EXT __extension__
#else
# define SECP256K1_GNUC_EXT
#endif

/* If SECP256K1_{LITTLE,BIG}_ENDIAN is not explicitly provided, infer from various other system macros. */
#if !defined(SECP256K1_LITTLE_ENDIAN) && !defined(SECP256K1_BIG_ENDIAN)
/* Inspired by https://github.com/rofl0r/endianness.h/blob/9853923246b065a3b52d2c43835f3819a62c7199/endianness.h#L52L73 */
# if (defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__) || \
     defined(_X86_) || defined(__x86_64__) || defined(__i386__) || \
     defined(__i486__) || defined(__i586__) || defined(__i686__) || \
     defined(__MIPSEL) || defined(_MIPSEL) || defined(MIPSEL) || \
     defined(__ARMEL__) || defined(__AARCH64EL__) || \
     (defined(__LITTLE_ENDIAN__) && __LITTLE_ENDIAN__ == 1) || \
     (defined(_LITTLE_ENDIAN) && _LITTLE_ENDIAN == 1) || \
     defined(_M_IX86) || defined(_M_AMD64) || defined(_M_ARM) /* MSVC */
#  define SECP256K1_LITTLE_ENDIAN
# endif
# if (defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__) || \
     defined(__MIPSEB) || defined(_MIPSEB) || defined(MIPSEB) || \
     defined(__MICROBLAZEEB__) || defined(__ARMEB__) || defined(__AARCH64EB__) || \
     (defined(__BIG_ENDIAN__) && __BIG_ENDIAN__ == 1) || \
     (defined(_BIG_ENDIAN) && _BIG_ENDIAN == 1)
#  define SECP256K1_BIG_ENDIAN
# endif
#endif
#if defined(SECP256K1_LITTLE_ENDIAN) == defined(SECP256K1_BIG_ENDIAN)
# error Please make sure that either SECP256K1_LITTLE_ENDIAN or SECP256K1_BIG_ENDIAN is set, see src/util.h.
#endif

/* Zero memory if flag == 1. Flag must be 0 or 1. Constant time. */
static SECP256K1_INLINE void secp256k1_memczero(void *s, size_t len, int flag) {
    unsigned char *p = (unsigned char *)s;
    /* Access flag with a volatile-qualified lvalue.
       This prevents clang from figuring out (after inlining) that flag can
       take only be 0 or 1, which leads to variable time code. */
    volatile int vflag = flag;
    unsigned char mask = -(unsigned char) vflag;
    while (len) {
        *p &= ~mask;
        p++;
        len--;
    }
}

static SECP256K1_INLINE int secp256k1_memcmp_var(const void *s1, const void *s2, size_t n) {
    const unsigned char *p1 = s1, *p2 = s2;
    size_t i;

    for (i = 0; i < n; i++) {
        int diff = p1[i] - p2[i];
        if (diff != 0) {
            return diff;
        }
    }
    return 0;
}

static SECP256K1_INLINE void secp256k1_int_cmov(int *r, const int *a, int flag) {
    unsigned int mask0, mask1, r_masked, a_masked;
    /* Access flag with a volatile-qualified lvalue.
       This prevents clang from figuring out (after inlining) that flag can
       take only be 0 or 1, which leads to variable time code. */
    volatile int vflag = flag;

    /* Casting a negative int to unsigned and back to int is implementation defined behavior */
    VERIFY_CHECK(*r >= 0 && *a >= 0);

    mask0 = (unsigned int)vflag + ~0u;
    mask1 = ~mask0;
    r_masked = ((unsigned int)*r & mask0);
    a_masked = ((unsigned int)*a & mask1);

    *r = (int)(r_masked | a_masked);
}

/* If USE_FORCE_WIDEMUL_{INT128,INT64} is set, use that wide multiplication implementation.
 * Otherwise use the presence of __SIZEOF_INT128__ to decide.
 */
#if defined(USE_FORCE_WIDEMUL_INT128)
# define SECP256K1_WIDEMUL_INT128 1
#elif defined(USE_FORCE_WIDEMUL_INT64)
# define SECP256K1_WIDEMUL_INT64 1
#elif defined(UINT128_MAX) || defined(__SIZEOF_INT128__)
# define SECP256K1_WIDEMUL_INT128 1
#else
# define SECP256K1_WIDEMUL_INT64 1
#endif
#if defined(SECP256K1_WIDEMUL_INT128)
# if !defined(UINT128_MAX) && defined(__SIZEOF_INT128__)
SECP256K1_GNUC_EXT typedef unsigned __int128 uint128_t;
SECP256K1_GNUC_EXT typedef __int128 int128_t;
#define UINT128_MAX ((uint128_t)(-1))
#define INT128_MAX ((int128_t)(UINT128_MAX >> 1))
#define INT128_MIN (-INT128_MAX - 1)
/* No (U)INT128_C macros because compilers providing __int128 do not support 128-bit literals.  */
# endif
#endif

#ifndef __has_builtin
#define __has_builtin(x) 0
#endif

/* Determine the number of trailing zero bits in a (non-zero) 32-bit x.
 * This function is only intended to be used as fallback for
 * secp256k1_ctz32_var, but permits it to be tested separately. */
static SECP256K1_INLINE int secp256k1_ctz32_var_debruijn(uint32_t x) {
    static const uint8_t debruijn[32] = {
        0x00, 0x01, 0x02, 0x18, 0x03, 0x13, 0x06, 0x19, 0x16, 0x04, 0x14, 0x0A,
        0x10, 0x07, 0x0C, 0x1A, 0x1F, 0x17, 0x12, 0x05, 0x15, 0x09, 0x0F, 0x0B,
        0x1E, 0x11, 0x08, 0x0E, 0x1D, 0x0D, 0x1C, 0x1B
    };
    return debruijn[((x & -x) * 0x04D7651F) >> 27];
}

/* Determine the number of trailing zero bits in a (non-zero) 64-bit x.
 * This function is only intended to be used as fallback for
 * secp256k1_ctz64_var, but permits it to be tested separately. */
static SECP256K1_INLINE int secp256k1_ctz64_var_debruijn(uint64_t x) {
    static const uint8_t debruijn[64] = {
        0, 1, 2, 53, 3, 7, 54, 27, 4, 38, 41, 8, 34, 55, 48, 28,
        62, 5, 39, 46, 44, 42, 22, 9, 24, 35, 59, 56, 49, 18, 29, 11,
        63, 52, 6, 26, 37, 40, 33, 47, 61, 45, 43, 21, 23, 58, 17, 10,
        51, 25, 36, 32, 60, 20, 57, 16, 50, 31, 19, 15, 30, 14, 13, 12
    };
    return debruijn[((x & -x) * 0x022FDD63CC95386D) >> 58];
}

/* Determine the number of trailing zero bits in a (non-zero) 32-bit x. */
static SECP256K1_INLINE int secp256k1_ctz32_var(uint32_t x) {
    VERIFY_CHECK(x != 0);
#if (__has_builtin(__builtin_ctz) || SECP256K1_GNUC_PREREQ(3,4))
    /* If the unsigned type is sufficient to represent the largest uint32_t, consider __builtin_ctz. */
    if (((unsigned)UINT32_MAX) == UINT32_MAX) {
        return __builtin_ctz(x);
    }
#endif
#if (__has_builtin(__builtin_ctzl) || SECP256K1_GNUC_PREREQ(3,4))
    /* Otherwise consider __builtin_ctzl (the unsigned long type is always at least 32 bits). */
    return __builtin_ctzl(x);
#else
    /* If no suitable CTZ builtin is available, use a (variable time) software emulation. */
    return secp256k1_ctz32_var_debruijn(x);
#endif
}

/* Determine the number of trailing zero bits in a (non-zero) 64-bit x. */
static SECP256K1_INLINE int secp256k1_ctz64_var(uint64_t x) {
    VERIFY_CHECK(x != 0);
#if (__has_builtin(__builtin_ctzl) || SECP256K1_GNUC_PREREQ(3,4))
    /* If the unsigned long type is sufficient to represent the largest uint64_t, consider __builtin_ctzl. */
    if (((unsigned long)UINT64_MAX) == UINT64_MAX) {
        return __builtin_ctzl(x);
    }
#endif
#if (__has_builtin(__builtin_ctzll) || SECP256K1_GNUC_PREREQ(3,4))
    /* Otherwise consider __builtin_ctzll (the unsigned long long type is always at least 64 bits). */
    return __builtin_ctzll(x);
#else
    /* If no suitable CTZ builtin is available, use a (variable time) software emulation. */
    return secp256k1_ctz64_var_debruijn(x);
#endif
}

#endif /* SECP256K1_UTIL_H */