Faster fmpz/int conversion using from_bytes/to_bytes

Author: remyoudompheng

src/flint/types/arb.pyx

@@ -31,6 +31,7 @@ from flint.flintlib.functions.acb_dirichlet cimport *
 
 cimport libc.stdlib
 cimport cython
+import sys  # no-cython-lint
 
 ctx = thectx
 

src/flint/types/fmpz.pxd

@@ -1,20 +1,46 @@
 from cpython.long cimport PyLong_Check
 from flint.flint_base.flint_base cimport flint_scalar
 from flint.utils.conversion cimport chars_from_str
-from flint.flintlib.types.flint cimport slong, pylong_as_slong
+from flint.flintlib.types.flint cimport slong, ulong, pylong_as_slong
 from flint.flintlib.types.flint cimport PyObject
-from flint.flintlib.functions.fmpz cimport fmpz_t, fmpz_set_str, fmpz_set_si
+from flint.flintlib.functions.fmpz cimport fmpz_t, fmpz_set_si, fmpz_set_signed_ui_array
+import sys
 
 cdef int fmpz_set_any_ref(fmpz_t x, obj)
 cdef fmpz_get_intlong(fmpz_t x)
 
+cdef extern from "byteswap.h":
+    """
+    #if FLINT_BITS == 32
+    #define bswap_ulong bswap_32
+    #elif FLINT_BITS == 64
+    #define bswap_ulong bswap_64
+    #else
+    #error FLINT_BITS must be 32 or 64
+    #endif
+    """
+    ulong bswap_ulong(ulong x)
+
 cdef inline int fmpz_set_pylong(fmpz_t x, obj):
     cdef int overflow
     cdef slong longval
+    cdef slong size
+    cdef bytes b
+    cdef ulong *words
+
     longval = pylong_as_slong(<PyObject*>obj, &overflow)
     if overflow:
-        s = "%x" % obj
-        fmpz_set_str(x, chars_from_str(s), 16)
+        # make sure the sign bit fits
+        # we need sizeof(ulong) * size > obj.bit_length()
+        size = obj.bit_length() // sizeof(ulong) + 1
+        b = obj.to_bytes(sizeof(ulong) * size, "little", signed=True)
+        # b is a local Python object, we access the internal pointer
+        words = <ulong*>(<char *>b)
+        # sys must be imported by the caller
+        if sys.byteorder == "big":
+            for i in range(size):
+                words[i] = bswap_ulong(words[i])
+        fmpz_set_signed_ui_array(x, words, size)
     else:
         fmpz_set_si(x, longval)
 

src/flint/types/fmpz.pyx

@@ -2,7 +2,8 @@ from flint.flint_base.flint_base cimport flint_scalar
 from flint.utils.typecheck cimport typecheck
 from flint.utils.conversion cimport chars_from_str
 from flint.utils.conversion cimport str_from_chars, _str_trunc
-cimport libc.stdlib
+from libc.stdlib cimport malloc, free
+import sys
 
 from flint.flintlib.types.flint cimport FMPZ_REF, FMPZ_TMP, FMPZ_UNKNOWN, COEFF_IS_MPZ
 from flint.flintlib.functions.flint cimport flint_free
@@ -14,16 +15,23 @@ from flint.flintlib.functions.partitions cimport *
 
 from flint.utils.flint_exceptions import DomainError
 
-
 cdef fmpz_get_intlong(fmpz_t x):
     """
     Convert fmpz_t to a Python int or long.
     """
-    cdef char * s
+    cdef slong size
+    cdef ulong * words
     if COEFF_IS_MPZ(x[0]):
-        s = fmpz_get_str(NULL, 16, x)
-        v = int(str_from_chars(s), 16)
-        flint_free(s)
+        # make sure the sign bit fits
+        # we need sizeof(ulong) * size > fmpz_bits(x)
+        size = fmpz_bits(x) // sizeof(ulong) + 1
+        words = <ulong *>malloc(size * sizeof(ulong))
+        fmpz_get_signed_ui_array(words, size, x)
+        if sys.byteorder == "big":
+            for i in range(size):
+                words[i] = bswap_ulong(words[i])
+        v = int.from_bytes((<char *>words)[:size * sizeof(ulong)], "little", signed=True)
+        free(words)
         return v
     else:
         return <slong>x[0]