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-rw-r--r--miscutils/bc.c13
1 files changed, 8 insertions, 5 deletions
diff --git a/miscutils/bc.c b/miscutils/bc.c
index e12a20a..a5d8734 100644
--- a/miscutils/bc.c
+++ b/miscutils/bc.c
@@ -5,7 +5,7 @@
* Original code copyright (c) 2018 Gavin D. Howard and contributors.
*/
//TODO:
-// maybe implement a^b for non-integer b?
+// maybe implement a^b for non-integer b? (see zbc_num_p())
#define DEBUG_LEXER 0
#define DEBUG_COMPILE 0
@@ -2163,6 +2163,9 @@ static FAST_FUNC BC_STATUS zbc_num_p(BcNum *a, BcNum *b, BcNum *restrict c, size
if (b->num[i] != 0)
RETURN_STATUS(bc_error("not an integer"));
+// a^b for non-integer b (for a>0) can be implemented as exp(ln(a)*b).
+// Possibly better precision would be given by a^int(b) * exp(ln(a)*frac(b)).
+
if (b->len == 0) {
bc_num_one(c);
RETURN_STATUS(BC_STATUS_SUCCESS);
@@ -2199,11 +2202,11 @@ static FAST_FUNC BC_STATUS zbc_num_p(BcNum *a, BcNum *b, BcNum *restrict c, size
//but it can be improved to detect zero results etc. Example: with scale=0,
//result of 0.01^N for any N>1 is 0: 0.01^2 = 0.0001 ~= 0.00 (trunc to scale)
//then this would matter:
- // if (new_scale >= pow) is false, we had overflow, correct
- // "new_scale" value is larger than ULONG_MAX, thus larger
- // than any possible current value of "scale",
+ // if a_rdx != 0 and new_scale < pow, we had overflow,
+ // correct "new_scale" value is larger than ULONG_MAX,
+ // thus larger than any possible current value of "scale",
// thus "scale = new_scale" should not be done:
- if (new_scale >= pow)
+ if (a_rdx == 0 || new_scale >= pow)
if (new_scale < scale)
scale = new_scale;
}