From: "kyanagi (Kouhei Yanagita)" Date: 2022-05-27T22:23:58+00:00 Subject: [ruby-core:108724] [Ruby master Feature#18809] Add Numeric#ceildiv Issue #18809 has been reported by kyanagi (Kouhei Yanagita). ---------------------------------------- Feature #18809: Add Numeric#ceildiv https://bugs.ruby-lang.org/issues/18809 * Author: kyanagi (Kouhei Yanagita) * Status: Open * Priority: Normal ---------------------------------------- pull request: https://github.com/ruby/ruby/pull/5965 I have needed to implement "rounding up division" several times. ("rounding up division" means getting a quotient of division which is rounded up to the nearest integer.) Typically, this is implemented as follows: ``` ruby # notice that b > 0 is assumed def rounding_up_division(a, b) (a + b - 1) / b end ``` But for me, this is difficult to write without careful consideration. Every time I implement this, I need to think for a few minutes on paper. So I propose to add a new method `Numeric#ceildiv`. Typical examples where this is necessary are counting groups and pagination. e.g. There are 123 items. If you display 10 items on each page, how many pages are there? ``` ruby 123.ceildiv(10) # => 13 ``` We can find several examples of this division also in the Ruby's source code. (Try `grep -r -E -e '([^ ]+) *- *1\) */ *\1' .`) ``` ./internal.h:#define roomof(x, y) (((x) + (y) - 1) / (y)) ./array.c: len = (len + ustep - 1) / ustep; ./include/ruby/internal/memory.h: const size_t cnt = (total_size + sizeof(VALUE) - 1) / sizeof(VALUE); ./ext/bigdecimal/missing/dtoa.c:#define PRIVATE_mem ((PRIVATE_MEM+sizeof(double)-1)/sizeof(double)) ./ext/bigdecimal/bigdecimal.c: nc += (nc + mc - 1) / mc + 1; ./ext/bigdecimal/bigdecimal.c: mx = (mx + BASE_FIG - 1) / BASE_FIG; /* Determine allocation unit. */ ./ext/bigdecimal/bigdecimal.c: mf = (mf + BASE_FIG - 1) / BASE_FIG + 2; /* Needs 1 more for div */ ./ext/bigdecimal/bigdecimal.c: nalloc = (ni + nf + BASE_FIG - 1) / BASE_FIG + 1; /* set effective allocation */ ./ext/bigdecimal/bigdecimal.c: size_t const round_limit = (VpGetPrecLimit() + BASE_FIG - 1) / BASE_FIG; ./ext/bigdecimal/bigdecimal.c: if ((ix + BASE_FIG - 1) / BASE_FIG > ixDigit + 1) return 0; ./ext/bigdecimal/bits.h:#define roomof(x, y) (((x) + (y) - 1) / (y)) ./internal/numeric.h: VALUE values[(SIZEOF_DOUBLE + SIZEOF_VALUE - 1) / SIZEOF_VALUE]; ./regcomp.c: OnigDistance str_len = (byte_len + mb_len - 1) / mb_len; ./bignum.c: size_t num_bdigits = (num_bits + BITSPERDIG - 1) / BITSPERDIG; ./missing/dtoa.c:#define PRIVATE_mem ((PRIVATE_MEM+sizeof(double)-1)/sizeof(double)) ./numeric.c: char buf[float_dig + (decimal_mant + CHAR_BIT - 1) / CHAR_BIT + 10]; ./gc.c:#define CEILDIV(i, mod) (((i) + (mod) - 1)/(mod)) ``` Naming: I was not sure whether to name it `ceildiv` or `divceil` because there are both `divmod` and `fdiv`. Since `divmod` is a method that returns two elements, the quotient and the remainder, while `fdiv` is a method that performs Float division, I decided to follow `fdiv`. -- https://bugs.ruby-lang.org/ Unsubscribe: