2 files changed, 20 insertions(+), 34 deletions(-)

M sha_consts/sha_consts.c
M sha_consts/sha_consts.h

@@ 124,8 124,8 @@ void frac64(const unsigned long int *primes, int n)
 
     mpfr_t prime, cbrt_prime;
 
-    /* We assume 113 bits of precision according to IEEE-754 Quadruple precision
-     * binary 128 bit floating point numbers */
+    /* We assume 113 bits of precision according to IEEE-754 Quadruple
+     * precision binary 128 bit floating point numbers */
     mpfr_prec_t prec = 113;
 
     mpfr_inits2(prec, prime, cbrt_prime, (mpfr_ptr) 0);


@@ 137,34 137,27 @@ void frac64(const unsigned long int *primes, int n)
         /* MPFR's cube root function */
         mpfr_cbrt(cbrt_prime, prime, MPFR_RNDN);
 
-        /* This is an attempt to get raw significand bytes out of MPFR */
+        /*
+         * This is an attempt to get raw significand bytes out of MPFR
+         */
 
-        /* The `mpfr_custom_get_significand()` function returns a pointer to
-         * the significand in memory. We shall cast this into a custom type
-         * which is able to handle 128 bits of data and we can then access its
-         * higher order bits and lower order bits and extract the fractional
-         * part accordingly. */
-        sig128_t significand = *(sig128_t *)
-                               mpfr_custom_get_significand(cbrt_prime);
+        /* The  `mpfr_custom_get_significand()`  function   returns  a
+         * pointer to the  significand in memory which in this case is
+         * 128  bits  wide.  I don't know  how  good  the support  for
+         * `__int128` is,  but at least  GCC and clang  are  happy  to
+         * compile this for x86_64  with GCC slightly bitching because
+         * of  `-Wpedantic`  which is fixed by prefixing the type with
+         * `__extension__`.  Hence I'm  ditching  the idea of  using a
+         * special struct and figuring out the endianness BS and using
+         * `__int128`. Let's see what breaks!
+         */
+        __extension__ unsigned __int128 significand = *(unsigned __int128 *)
+            mpfr_custom_get_significand(cbrt_prime);
         int exponent = mpfr_custom_get_exp(cbrt_prime);
 
-        /* Due to MPFR preserving endianess throughout the length of the
-         * significand, the upper and lower 64-bit words need to be swapped in
-         * case the machine is little endian.
-         *
-         * Here we deternine the endianess in a quick and dirty way: */
-        int end_check = 1;
-        if ( *(uint8_t *) &end_check ) {
-            /* We detect little endian system */
-            uint64_t temp = significand.upper;
-            significand.upper = significand.lower;
-            significand.lower = temp;
-        }
-
-        /* Then shift the entire 128 bit word left by the exponent */
-        uint64_t fractional_part = significand.upper << exponent
-                                   |
-                                   significand.lower >> (64 - exponent);
+        /* Shift the entire 128 bit word left by the exponent and then
+         * take the most significand 64 bits. */
+        uint64_t fractional_part = significand >> (64 - exponent);
 
         printf("0x%016"PRIx64"\n", fractional_part);
     }

@@ 1,13 1,6 @@
 #ifndef _SHA_CONSTS_H
 # define _SHA_CONSTS_H
 
-# include <stdint.h>
-
-typedef struct {
-    uint64_t upper;
-    uint64_t lower;
-} sig128_t;
-
 void frac32(const unsigned long int *, int);
 void frac64(const unsigned long int *, int);