Remove usage of malloc() from fp_prime_random_ex.

This is the only instance of dynamic memory in TFM. It can be avoided
by writing directly into the dp[] array, and it does not violate C
aliasing rules which specifically allow access on objects through char*.
It does not matter the platform-specific representation of digits since
we are filling them with random data anyway.

src/headers/tfm.h

@@ -1,10 +1,10 @@
 /* TomsFastMath, a fast ISO C bignum library.
- * 
+ *
  * This project is meant to fill in where LibTomMath
  * falls short.  That is speed ;-)
  *
  * This project is public domain and free for all purposes.
- * 
+ *
  * Tom St Denis, tomstdenis@gmail.com
  */
 #ifndef TFM_H_
@@ -27,13 +27,13 @@
 /* externally define this symbol to ignore the default settings, useful for changing the build from the make process */
 #ifndef TFM_ALREADY_SET
 
-/* do we want the large set of small multiplications ? 
+/* do we want the large set of small multiplications ?
    Enable these if you are going to be doing a lot of small (<= 16 digit) multiplications say in ECC
    Or if you're on a 64-bit machine doing RSA as a 1024-bit integer == 16 digits ;-)
  */
 #define TFM_SMALL_SET
 
-/* do we want huge code 
+/* do we want huge code
    Enable these if you are doing 20, 24, 28, 32, 48, 64 digit multiplications (useful for RSA)
    Less important on 64-bit machines as 32 digits == 2048 bits
  */
@@ -81,7 +81,7 @@
 /* #define TFM_PRESCOTT */
 
 /* Do we want timing resistant fp_exptmod() ?
- * This makes it slower but also timing invariant with respect to the exponent 
+ * This makes it slower but also timing invariant with respect to the exponent
  */
 /* #define TFM_TIMING_RESISTANT */
 
@@ -106,7 +106,7 @@
 
 /* autodetect x86-64 and make sure we are using 64-bit digits with x86-64 asm */
 #if defined(__x86_64__)
-   #if defined(TFM_X86) || defined(TFM_SSE2) || defined(TFM_ARM) 
+   #if defined(TFM_X86) || defined(TFM_SSE2) || defined(TFM_ARM)
        #error x86-64 detected, x86-32/SSE2/ARM optimizations are not valid!
    #endif
    #if !defined(TFM_X86_64) && !defined(TFM_NO_ASM)
@@ -121,7 +121,7 @@
 
 /* try to detect x86-32 */
 #if defined(__i386__) && !defined(TFM_SSE2)
-   #if defined(TFM_X86_64) || defined(TFM_ARM) 
+   #if defined(TFM_X86_64) || defined(TFM_ARM)
        #error x86-32 detected, x86-64/ARM optimizations are not valid!
    #endif
    #if !defined(TFM_X86) && !defined(TFM_NO_ASM)
@@ -185,7 +185,7 @@
    #undef TFM_PPC32
    #undef TFM_PPC64
    #undef TFM_AVR32
-   #undef TFM_ASM   
+   #undef TFM_ASM
 #endif
 
 /* ECC helpers */
@@ -249,6 +249,7 @@
 #endif
    typedef ulong64            fp_digit;
    typedef unsigned long      fp_word __attribute__ ((mode(TI)));
+   #define DIGIT_SHIFT        6
 #else
    /* this is to make porting into LibTomCrypt easier :-) */
 #ifndef CRYPT
@@ -262,6 +263,7 @@
 #endif
    typedef unsigned long      fp_digit;
    typedef ulong64            fp_word;
+   #define DIGIT_SHIFT        5
 #endif
 
 /* # of digits this is */
@@ -290,7 +292,7 @@
 /* a FP type */
 typedef struct {
     fp_digit dp[FP_SIZE];
-    int      used, 
+    int      used,
              sign;
 } fp_int;
 
@@ -434,9 +436,9 @@ int fp_isprime(fp_int *a);
 /* callback for fp_prime_random, should fill dst with random bytes and return how many read [upto len] */
 typedef int tfm_prime_callback(unsigned char *dst, int len, void *dat);
 
-#define fp_prime_random(a, t, size, bbs, cb, dat) fp_prime_random_ex(a, t, ((size) * 8) + 1, (bbs==1)?TFM_PRIME_BBS:0, cb, dat)
+#define fp_prime_random(a, size, bbs, cb, dat) fp_prime_random_ex(a, ((size) * 8) + 1, (bbs==1)?TFM_PRIME_BBS:0, cb, dat)
 
-int fp_prime_random_ex(fp_int *a, int t, int size, int flags, tfm_prime_callback cb, void *dat);
+int fp_prime_random_ex(fp_int *a, int size, int flags, tfm_prime_callback cb, void *dat);
 
 /* radix conersions */
 int fp_count_bits(fp_int *a);

src/numtheory/fp_prime_random_ex.c

@@ -1,22 +1,28 @@
 /* TomsFastMath, a fast ISO C bignum library.
- * 
+ *
  * This project is meant to fill in where LibTomMath
  * falls short.  That is speed ;-)
  *
  * This project is public domain and free for all purposes.
- * 
+ *
  * Tom St Denis, tomstdenis@gmail.com
  */
 #include <tfm.h>
 
+#define fp_on_bitnum(a, bitnum) \
+    a->dp[(bitnum) >> DIGIT_SHIFT] |= 1 << ((bitnum) & (DIGIT_BIT-1));
+
+#define fp_off_bitnum(a, bitnum) \
+    a->dp[(bitnum) >> DIGIT_SHIFT] &= ~(1 << ((bitnum) & (DIGIT_BIT-1)));
+
 /* This is possibly the mother of all prime generation functions, muahahahahaha! */
-int fp_prime_random_ex(fp_int *a, int t, int size, int flags, tfm_prime_callback cb, void *dat)
+int fp_prime_random_ex(fp_int *a, int size, int flags, tfm_prime_callback cb, void *dat)
 {
-   unsigned char *tmp, maskAND, maskOR_msb, maskOR_lsb;
+   fp_digit maskAND_msb, maskOR_lsb;
-   int res, err, bsize, maskOR_msb_offset;
+   int res, err, bsize, dsize;
 
    /* sanity check the input */
-   if (size <= 1 || t <= 0) {
+   if (size <= 1) {
       return FP_VAL;
    }
 
@@ -25,26 +31,11 @@ int fp_prime_random_ex(fp_int *a, int t, int size, int flags, tfm_prime_callback
       flags |= TFM_PRIME_BBS;
    }
 
-   /* calc the byte size */
+   /* calc the digit size */
-   bsize = (size>>3)+(size&7?1:0);
+   dsize = (size + DIGIT_BIT - 1) >> DIGIT_SHIFT;
 
-   /* we need a buffer of bsize bytes */
+   /* calc the maskAND value for the MSbyte */
-   tmp = malloc(bsize);
+   maskAND_msb = FP_MASK >> ((DIGIT_BIT - (size & (DIGIT_BIT-1))) & (DIGIT_BIT-1));
-   if (tmp == NULL) {
-      return FP_MEM;
-   }
-
-   /* calc the maskAND value for the MSbyte*/
-   maskAND = 0xFF >> ((8 - (size & 7)) & 7);
-
-   /* calc the maskOR_msb */
-   maskOR_msb        = 0;
-   maskOR_msb_offset = (size - 2) >> 3;
-   if (flags & TFM_PRIME_2MSB_ON) {
-      maskOR_msb     |= 1 << ((size - 2) & 7);
-   } else if (flags & TFM_PRIME_2MSB_OFF) {
-      maskAND        &= ~(1 << ((size - 2) & 7));
-   }
 
    /* get the maskOR_lsb */
    maskOR_lsb         = 1;
@@ -54,21 +45,26 @@ int fp_prime_random_ex(fp_int *a, int t, int size, int flags, tfm_prime_callback
 
    do {
       /* read the bytes */
-      if (cb(tmp, bsize, dat) != bsize) {
+      if (cb((unsigned char*)&a->dp[0], dsize*DIGIT_BIT, dat) != dsize*DIGIT_BIT) {
-         err = FP_VAL;
+         return FP_VAL;
-         goto error;
       }
- 
+      a->used = dsize;
-      /* work over the MSbyte */
-      tmp[0]    &= maskAND;
-      tmp[0]    |= 1 << ((size - 1) & 7);
 
-      /* mix in the maskORs */
+      /* make sure the MSbyte has the required number of bits */
-      tmp[maskOR_msb_offset]   |= maskOR_msb;
+      a->dp[dsize-1]    &= maskAND_msb;
-      tmp[bsize-1]             |= maskOR_lsb;
 
-      /* read it in */
+      /* modify the LSbyte as requested */
-      fp_read_unsigned_bin(a, tmp, bsize);
+      a->dp[0]          |= maskOR_lsb;
+
+      /* turn on the MSbit to force the requested magnitude */
+      fp_on_bitnum(a, size-1);
+
+      /* modify the 2nd MSBit */
+      if (flags & TFM_PRIME_2MSB_ON) {
+          fp_on_bitnum(a, size-2);
+      } else if (flags & TFM_PRIME_2MSB_OFF) {
+          fp_off_bitnum(a, size-2);
+      }
 
       /* is it prime? */
       res = fp_isprime(a);
@@ -78,7 +74,7 @@ int fp_prime_random_ex(fp_int *a, int t, int size, int flags, tfm_prime_callback
          /* see if (a-1)/2 is prime */
          fp_sub_d(a, 1, a);
          fp_div_2(a, a);
- 
+
          /* is it prime? */
          res = fp_isprime(a);
       }
@@ -90,10 +86,7 @@ int fp_prime_random_ex(fp_int *a, int t, int size, int flags, tfm_prime_callback
       fp_add_d(a, 1, a);
    }
 
-   err = FP_OKAY;
+   return FP_OKAY;
-error:
-   free(tmp);
-   return err;
 }
 
 /* $Source$ */