VM: better version of bignum_to_fixnum_strict that doesn't allocate

diff --git a/vm/bignum.cpp b/vm/bignum.cpp
index b2b1109183de38e20270e6268669f512f74cad69..799099e3c6df7bf7380f379c44eb6836c8ca4aef 100644 (file)
--- a/vm/bignum.cpp
+++ b/vm/bignum.cpp
@@ -383,14 +383,15 @@ BIGNUM_TO_FOO(fixnum, fixnum, fixnum, cell)
 BIGNUM_TO_FOO(long_long, int64_t, int64_t, uint64_t)
 BIGNUM_TO_FOO(ulong_long, uint64_t, int64_t, uint64_t)
 
-/* does allocate memory */
+/* cannot allocate memory */
 fixnum factor_vm::bignum_to_fixnum_strict(bignum* bignum_in) {
-  fixnum fix = bignum_to_fixnum(bignum_in);
-  bignum* bignum_out = fixnum_to_bignum(fix);
-  GC_BIGNUM(bignum_out);
-  if (bignum_compare(bignum_in, bignum_out) != bignum_comparison_equal) {
+  fixnum len = BIGNUM_LENGTH(bignum_in);
+  bignum_digit_type *digits = BIGNUM_START_PTR(bignum_in);
+  if ((len == 1 && digits[0] > fixnum_max) || (len > 1)) {
     general_error(ERROR_OUT_OF_FIXNUM_RANGE, tag<bignum>(bignum_in), false_object);
   }
+  fixnum fix = bignum_to_fixnum(bignum_in);
+  FACTOR_ASSERT(fix <= fixnum_max && fix >= fixnum_min);
   return fix;
 }
 

diff --git a/vm/math.cpp b/vm/math.cpp
index 71ba13b803bd95cd09699c1e917146fda0b54fb3..e88145a2f29ee95e732ebfa734b3fd47823ee595 100644 (file)
--- a/vm/math.cpp
+++ b/vm/math.cpp
@@ -277,7 +277,7 @@ void factor_vm::primitive_bits_double() {
   ctx->push(allot_float(bits_double(to_unsigned_8(ctx->pop()))));
 }
 
-/* Allocates memory */
+/* Cannot allocate */
 fixnum factor_vm::to_fixnum(cell tagged) {
   switch (TAG(tagged)) {
     case FIXNUM_TYPE: