Bug #44995 [PATCH]: bcpowmod() should not have scale parameter (only 0 is supported)

Edit report at http://bugs.php.net/bug.php?id=44995&edit=1 ID: 44995 Patch added by: k.schroeder@php.net Reported by: nat at fishtrap dot co dot uk Summary: bcpowmod() should not have scale parameter (only 0 is supported) Status: Analyzed Type: Bug Package: BC math related Operating System: * PHP Version: 5.*, 6 (2009-09-20) Block user comment: N New Comment: The following patch has been added/updated: Patch Name: remove_scale_parameter_from_bcpowmod_bug44995 Revision: 1283200734 URL: http://bugs.php.net/patch-display.php?bug=44995&patch=remove_scale_parameter_from_bcpowmod_bug44995&revision=1283200734 Previous Comments: ------------------------------------------------------------------------ [2010-02-07 01:47:52] terrafrost at gmail dot com Related to this... <?php echo bcpowmod('3234', '32345', '22345', 0) . "\r\n"; echo bcpowmod('3234', '32345', '22345', 1); ?> That outputs the following: 17334 1140.8 It seems to me that the output of the above ought to either be this: Warning: bcpowmod() expects at most 3 parameters, 4 given ...or this: 17334 17334.0 ------------------------------------------------------------------------ [2009-09-20 14:43:23] sjoerd@php.net John Hasler said: The example in #44995 is wrong. "^" has higher precedence than "%" so "4^4%3" means "(4^4)%3" or "256%3", not "4^(4%3). The latter gives a runtime error in bc with scale=1, as it should as fractional exponents are not supported. From number.c: /* Raise BASE to the EXPO power, reduced modulo MOD. The result is placed in RESULT. If a EXPO is not an integer, only the integer part is used. */ ... ... ... /* Check the base for scale digits. */ if (base->n_scale != 0) bc_rt_warn ("non-zero scale in base"); /* Check the exponent for scale digits. */ if (exponent->n_scale != 0) { bc_rt_warn ("non-zero scale in exponent"); bc_divide (exponent, _one_, &exponent, 0); /*truncate */ } /* Check the modulus for scale digits. */ if (mod->n_scale != 0) bc_rt_warn ("non-zero scale in modulus"); ... ... ... As you can see, non-zero scale is not supported. Thus the bug is in bcpowmod(). It should not accept a scale, and the documentation should say so. ------------------------------------------------------------------------ [2009-09-19 18:22:41] sjoerd@php.net This seems to be a bug in the bc library. I asked jhasler to look into it. ------------------------------------------------------------------------ [2008-05-14 16:26:56] nat at fishtrap dot co dot uk Description: ------------ When using the 4th optional parameter of bcpowmod. The answer is always zero and does not match the answer using bc directly. This is also true if you set the scale using bcscale(1). In short if the scale is non zero I can't find any way of getting anything apart from zero as the result. Reproduce code: --------------- echo bcpowmod("4", "4", "3", 1 ) ,PHP_EOL; Expected result: ---------------- 0.1 in bc scale =1; 4^4%3; .1 Actual result: -------------- 0.0 ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/bug.php?id=44995&edit=1