Rename M_HASH_SEED into M_USE_HASH_SEED

as it a user overridable macro
(API break).

README.md

@@ -5950,12 +5950,19 @@ the string is truncated. Example:
 
 #### HASH Functions
 
-##### M\_HASH\_SEED --> size\_t
+##### M\_USE\_HASH\_SEED
 
-User shall overwrite this macro by a random seed (of type size\_t) before including
+A User modifiable macro defining the initial random seed (of type size\_t).
-the header m-core.h that hash functions use this variable
+It shall be define before including any header of M\*LIB,
-as the seed for their hash computation. 
+so that hash functions use this variable
-If no user macro is defined, the default is to use 0,
+as their initial seed for their hash computation of an object. 
+It can be used to generate less predictable hash values at runtime, 
+which may protect against 
+[DOS dictionary attacks](https://events.ccc.de/congress/2011/Fahrplan/attachments/2007_28C3_Effective_DoS_on_web_application_platforms.pdf).
+It shall be unique for a running instance of M\*LIB.
+Note that using a random seed is not enough to protect efficienly againt
+such attacks. A cryptographic secure hash may be also needed.
+If it is not defined, the default is to use the value 0,
 making all hash computations predictable.
 
 ##### M\_HASH\_DECL(hash)
@@ -7686,6 +7693,12 @@ Define the default size of a segment for a deque structure.
 
 Default value: 8 elements.
 
+### M\_USE\_HASH\_SEED
+
+Define the seed to inject to the hash computation of an object.
+
+Default value: 0 (predictable hash)
+
 ### M\_MEMORY\_ALLOC
 
 See [m-core.h](#m-core)

doc/API.txt

@@ -63,4 +63,5 @@ V0.5.*: * M_INVERT is renamed into M_REVERSE to be more coherent with the REVERS
         * Remove ALGO_INIT_VA & M_ALG0_LET_INIT_VAI of m-algo as it has been deprecated. Use of M_LET instead.
         * Some Internal name of user modifiable macros have been renamed to be properly 
         customizable by the user.
+        * Rename M_HASH_SEED into M_USE_HASH_SEED as it is a user macro.
         

example/ex-multi03.c

@@ -4,7 +4,7 @@
 /* Register a dynamic seed to M*LIB hash function. 
    This shall be done before any M*LIB header inclusion. */
 unsigned long long rand_seed;
-#define M_HASH_SEED rand_seed
+#define M_USE_HASH_SEED rand_seed
 
 #include "m-array.h"
 #include "m-dict.h"

m-core.h

@@ -2293,8 +2293,8 @@ m_core_snprintf(char *str, size_t size, const char *format, ...)
    so that the hash are not easily predictible by an attacker.
    See https://events.ccc.de/congress/2011/Fahrplan/attachments/2007_28C3_Effective_DoS_on_web_application_platforms.pdf
 */
-#ifndef M_HASH_SEED
+#ifndef M_USE_HASH_SEED
-# define M_HASH_SEED 0UL
+# define M_USE_HASH_SEED 0UL
 #endif
 
 #if   defined(M_USE_DJB_HASH)
@@ -2324,7 +2324,7 @@ m_core_snprintf(char *str, size_t size, const char *format, ...)
 #define M_HASH_CALC(h1,h2)  (((h1) * 0x811C9DC5UL) ^ (h2))
 #endif
 
-#define M_HASH_DECL(hash)   size_t hash = M_HASH_INIT ^ M_HASH_SEED
+#define M_HASH_DECL(hash)   size_t hash = M_HASH_INIT ^ M_USE_HASH_SEED
 #define M_HASH_UP(hash,h)   do { hash = (size_t) M_HASH_CALC(hash, (h)); } while (0)
 #define M_HASH_FINAL(hash)  ( (hash) >> (sizeof(size_t)*CHAR_BIT/2) | (hash) )
 
@@ -2454,7 +2454,7 @@ static inline uint32_t
 m_core_hash (const void *str, size_t length)
 {
   const uint32_t prime = 709607U;
-  uint32_t hash32 = 2166136261U ^ M_HASH_SEED;
+  uint32_t hash32 = 2166136261U ^ M_USE_HASH_SEED;
   const uint8_t *p = (const uint8_t *)str;
 
   M_ASSERT (str != NULL || length == 0);
@@ -2487,7 +2487,7 @@ static inline uint64_t
 m_core_hash (const void *str, size_t length)
 {
   const uint64_t prime = 1099511628211ULL;
-  uint64_t hash64 = 14695981039346656037ULL ^ M_HASH_SEED;
+  uint64_t hash64 = 14695981039346656037ULL ^ M_USE_HASH_SEED;
   const uint8_t *p = M_ASSIGN_CAST(const uint8_t *, str);
 
   M_ASSERT (str != NULL || length == 0);
@@ -2540,8 +2540,8 @@ static inline size_t m_core_cstr_hash(const char str[])
    NOTE: Default case is not safe if the type is defined with the '[1]' trick. */
 #define M_HASH_POD_DEFAULT(a)   m_core_hash((const void*) &(a), sizeof (a))
 #if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
-#define M_HASH_INT32(a) ( (a) ^ ((a) << 11) ^ M_HASH_SEED )
+#define M_HASH_INT32(a) ( (a) ^ ((a) << 11) ^ M_USE_HASH_SEED )
-#define M_HASH_INT64(a) ( ( (a) >> 33 ) ^ (a) ^ ((a) << 11) ^ M_HASH_SEED )
+#define M_HASH_INT64(a) ( ( (a) >> 33 ) ^ (a) ^ ((a) << 11) ^ M_USE_HASH_SEED )
 #define M_HASH_DEFAULT(a)                                                     \
   (size_t) _Generic((a)+0,                                                    \
            int32_t:  M_HASH_INT32((uint32_t) M_AS_TYPE(int32_t, a)),          \