1  /***********************************************************************
 2   * Copyright (c) 2017 Andrew Poelstra                                  *
 3   * Distributed under the MIT software license, see the accompanying    *
 4   * file COPYING or https://www.opensource.org/licenses/mit-license.php.*
 5   ***********************************************************************/
 6  
 7  #ifndef SECP256K1_SCRATCH_IMPL_H
 8  #define SECP256K1_SCRATCH_IMPL_H
 9  
10  #include "util.h"
11  #include "scratch.h"
12  
13  static secp256k1_scratch* secp256k1_scratch_create(const secp256k1_callback* error_callback, size_t size) {
14      const size_t base_alloc = ROUND_TO_ALIGN(sizeof(secp256k1_scratch));
15      void *alloc = checked_malloc(error_callback, base_alloc + size);
16      secp256k1_scratch* ret = (secp256k1_scratch *)alloc;
17      if (ret != NULL) {
18          memset(ret, 0, sizeof(*ret));
19          memcpy(ret->magic, "scratch", 8);
20          ret->data = (void *) ((char *) alloc + base_alloc);
21          ret->max_size = size;
22      }
23      return ret;
24  }
25  
26  static void secp256k1_scratch_destroy(const secp256k1_callback* error_callback, secp256k1_scratch* scratch) {
27      if (scratch != NULL) {
28          if (secp256k1_memcmp_var(scratch->magic, "scratch", 8) != 0) {
29              secp256k1_callback_call(error_callback, "invalid scratch space");
30              return;
31          }
32          VERIFY_CHECK(scratch->alloc_size == 0); /* all checkpoints should be applied */
33          memset(scratch->magic, 0, sizeof(scratch->magic));
34          free(scratch);
35      }
36  }
37  
38  static size_t secp256k1_scratch_checkpoint(const secp256k1_callback* error_callback, const secp256k1_scratch* scratch) {
39      if (secp256k1_memcmp_var(scratch->magic, "scratch", 8) != 0) {
40          secp256k1_callback_call(error_callback, "invalid scratch space");
41          return 0;
42      }
43      return scratch->alloc_size;
44  }
45  
46  static void secp256k1_scratch_apply_checkpoint(const secp256k1_callback* error_callback, secp256k1_scratch* scratch, size_t checkpoint) {
47      if (secp256k1_memcmp_var(scratch->magic, "scratch", 8) != 0) {
48          secp256k1_callback_call(error_callback, "invalid scratch space");
49          return;
50      }
51      if (checkpoint > scratch->alloc_size) {
52          secp256k1_callback_call(error_callback, "invalid checkpoint");
53          return;
54      }
55      scratch->alloc_size = checkpoint;
56  }
57  
58  static size_t secp256k1_scratch_max_allocation(const secp256k1_callback* error_callback, const secp256k1_scratch* scratch, size_t objects) {
59      if (secp256k1_memcmp_var(scratch->magic, "scratch", 8) != 0) {
60          secp256k1_callback_call(error_callback, "invalid scratch space");
61          return 0;
62      }
63      /* Ensure that multiplication will not wrap around */
64      if (ALIGNMENT > 1 && objects > SIZE_MAX/(ALIGNMENT - 1)) {
65          return 0;
66      }
67      if (scratch->max_size - scratch->alloc_size <= objects * (ALIGNMENT - 1)) {
68          return 0;
69      }
70      return scratch->max_size - scratch->alloc_size - objects * (ALIGNMENT - 1);
71  }
72  
73  static void *secp256k1_scratch_alloc(const secp256k1_callback* error_callback, secp256k1_scratch* scratch, size_t size) {
74      void *ret;
75      size_t rounded_size;
76  
77      rounded_size = ROUND_TO_ALIGN(size);
78      /* Check that rounding did not wrap around */
79      if (rounded_size < size) {
80          return NULL;
81      }
82      size = rounded_size;
83  
84      if (secp256k1_memcmp_var(scratch->magic, "scratch", 8) != 0) {
85          secp256k1_callback_call(error_callback, "invalid scratch space");
86          return NULL;
87      }
88  
89      if (size > scratch->max_size - scratch->alloc_size) {
90          return NULL;
91      }
92      ret = (void *) ((char *) scratch->data + scratch->alloc_size);
93      memset(ret, 0, size);
94      scratch->alloc_size += size;
95  
96      return ret;
97  }
98  
99  #endif