(defn frequencies
"Returns a map from distinct items in coll to the number of times
they appear."
{:added "1.2"
:static true}
[coll]
(persistent!
(reduce (fn [counts x]
(assoc! counts x (inc (get counts x 0))))
(transient {}) coll)))
[C]cat sum.c #include <stdio.h> int main(void) { unsigned long long sum = 0, i; for (i = 0; i <= 1000000000; i++) //one billion sum += i; printf("%lld\n", sum); //500000000500000000 return 0; }
[C]time ./a.out 500000000500000000
real 0m0.003s user 0m0.001s sys 0m0.001s [C]gcc -O3 -S sum.c [C]cat sum.s .section __TEXT,__text,regular,pure_instructions .globl _main .align 4, 0x90 _main: Leh_func_begin1: pushq %rbp Ltmp0: movq %rsp, %rbp Ltmp1: leaq L_.str(%rip), %rdi movabsq $500000000500000000, %rsi xorb %al, %al callq _printf xorl %eax, %eax popq %rbp ret