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Less pessimal scm_integer_sub_zi

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* libguile/integers.c (scm_integer_sub_zi): Only delegate to
scm_integer_add_ii if y is negative.
This commit is contained in:
Andy Wingo 2022-01-09 20:48:45 +01:00
parent ad6811a12b
commit 2723513712
1 changed files with 16 additions and 4 deletions
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20
libguile/integers.c
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@ -2875,10 +2875,22 @@ scm_integer_sub_iz (scm_t_inum x, struct scm_bignum *y)
SCM
scm_integer_sub_zi (struct scm_bignum *x, scm_t_inum y)
{
// Assumes that -INUM_MIN can fit in a scm_t_inum, even if that
// scm_t_inum is not fixable, and that scm_integer_add_ii can handle
// scm_t_inum inputs outside the fixable range.
return scm_integer_add_zi (x, -y);
if (y == 0)
return scm_from_bignum (x);
if (y < 0)
// Assumes that -INUM_MIN can fit in a scm_t_inum, even if that
// scm_t_inum is not fixable, and that scm_integer_add_ii can handle
// scm_t_inum inputs outside the fixable range.
return scm_integer_add_zi (x, -y);
mpz_t result, zx;
mpz_init (result);
alias_bignum_to_mpz (x, zx);
mpz_sub_ui (result, zx, y);
scm_remember_upto_here_1 (x);
// FIXME: We know that if X is negative, no need to check if
// result is fixable.
return take_mpz (result);
}
SCM