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i'm wondering now is where does the speed come from.

Perhaps the simplest way to demonstrate the difference is to look at the number of opcodes generated in order to compare and count two sets of 64 bits stored as: two arrays; two strings of ascii 1s and 0s; two bitstrings of 64 bits each. You don't need to understand the opcodes to see the reduction.

Moving as much of the work (looping) into the optimised, compiled-C, opcodes just saves huge swaths of time and processor:

  1. Arrays:
    C:\test>perl -MO=Terse -E"@a=map{int rand 2}1..64;@b=map{int rand 2}1. +.64; for my$a(@a){ for my $b(@b){ $a==$b and ++$count }}" LISTOP (0x34e7c58) leave [1] OP (0x34eec40) enter COP (0x34e7c98) nextstate BINOP (0x34e7d00) aassign [9] UNOP (0x34e7d70) null [142] OP (0x34e7d40) pushmark LOGOP (0x34e7e90) mapwhile [8] LISTOP (0x34e7f00) mapstart OP (0x34e7ed0) pushmark UNOP (0x34e7e58) null UNOP (0x34e7f40) null LISTOP (0x34e80d0) scope OP (0x34e8110) null [177] UNOP (0x34e8178) int [4] UNOP (0x34e81b0) rand [3] SVOP (0x34e81e8) const [7] IV +(0x33cca88) 2 UNOP (0x34e7f78) rv2av SVOP (0x34e7e20) const [26] AV (0x33c7570) UNOP (0x34e7de0) null [142] OP (0x34e7db0) pushmark UNOP (0x34e8220) rv2av [2] PADOP (0x34e8258) gv GV (0xa76c8) *a COP (0x34e7660) nextstate BINOP (0x34e76c8) aassign [18] UNOP (0x34e7738) null [142] OP (0x34e7708) pushmark LOGOP (0x34e7858) mapwhile [17] LISTOP (0x34e78c8) mapstart OP (0x34e7898) pushmark UNOP (0x34e7820) null UNOP (0x34e7908) null LISTOP (0x34e7a98) scope OP (0x34e7ad8) null [177] UNOP (0x34e7b40) int [13] UNOP (0x34e7b78) rand [12] SVOP (0x34e7bb0) const [16] IV + (0x33c6e30) 2 UNOP (0x34e7940) rv2av SVOP (0x34e77e8) const [27] AV (0x33c6830) UNOP (0x34e77a8) null [142] OP (0x34e7778) pushmark UNOP (0x34e7be8) rv2av [11] PADOP (0x34e7c20) gv GV (0x33c6f40) *b COP (0x34eecb0) nextstate BINOP (0x34eed18) leaveloop LOOP (0x34eee30) enteriter [19] OP (0x34eee88) null [3] UNOP (0x34eef28) null [142] OP (0x34eeef8) pushmark UNOP (0x34ef568) rv2av [21] PADOP (0x34e75b8) gv GV (0xa76c8) *a UNOP (0x34eed58) null LOGOP (0x34eed90) and OP (0x34eee00) iter LISTOP (0x34eef68) lineseq COP (0x34eefa8) nextstate BINOP (0x34ef010) leaveloop LOOP (0x34ef128) enteriter [22] OP (0x34ef180) null [3] UNOP (0x34ef220) null [142] OP (0x34ef1f0) pushmark UNOP (0x34ef4c8) rv2av [24] PADOP (0x34ef500) gv GV (0x33c6f4 +0) *b UNOP (0x34ef050) null LOGOP (0x34ef088) and OP (0x34ef0f8) iter LISTOP (0x34ef260) lineseq COP (0x34ef2a0) nextstate UNOP (0x34ef308) null LOGOP (0x34ef340) and BINOP (0x34ef428) eq OP (0x34ef498) padsv [ +19] OP (0x34ef468) padsv [ +22] UNOP (0x34ef380) preinc UNOP (0x34ef3b8) null +[15] PADOP (0x34ef3f0) +gvsv GV (0x33c5ed0) *count OP (0x34ef0c8) unstack OP (0x34eedd0) unstack -e syntax OK
  2. Strings:
    C:\test>perl -MO=Terse -E"$a=join'',map{int rand 2}1..64;@b=map{int ra +nd 2}1..64; $count=($a&$b)=~tr[1][]" LISTOP (0x3447bc0) leave [1] OP (0x344f178) enter COP (0x3447c00) nextstate BINOP (0x3447c68) sassign LISTOP (0x3447cd8) join [8] OP (0x3447ca8) pushmark SVOP (0x3448118) const [22] PV (0x332ca20) "" LOGOP (0x3447d88) mapwhile [7] LISTOP (0x3447df8) mapstart OP (0x3447dc8) pushmark UNOP (0x3447d50) null UNOP (0x3447e38) null LISTOP (0x3447fc8) scope OP (0x3448008) null [177] UNOP (0x3448070) int [3] UNOP (0x34480a8) rand [2] SVOP (0x34480e0) const [6] IV +(0x332cb58) 2 UNOP (0x3447e70) rv2av SVOP (0x3447d18) const [23] AV (0x3327640) UNOP (0x3448150) null [15] PADOP (0x3448188) gvsv GV (0xa76a8) *a COP (0x34475c8) nextstate BINOP (0x3447630) aassign [17] UNOP (0x34476a0) null [142] OP (0x3447670) pushmark LOGOP (0x34477c0) mapwhile [16] LISTOP (0x3447830) mapstart OP (0x3447800) pushmark UNOP (0x3447788) null UNOP (0x3447870) null LISTOP (0x3447a00) scope OP (0x3447a40) null [177] UNOP (0x3447aa8) int [12] UNOP (0x3447ae0) rand [11] SVOP (0x3447b18) const [15] IV + (0x3326f00) 2 UNOP (0x34478a8) rv2av SVOP (0x3447750) const [24] AV (0x3326900) UNOP (0x3447710) null [142] OP (0x34476e0) pushmark UNOP (0x3447b50) rv2av [10] PADOP (0x3447b88) gv GV (0x3327010) *b COP (0x344f1e8) nextstate BINOP (0x344f250) sassign UNOP (0x344f290) null BINOP (0x344f3e8) bit_and [21] UNOP (0x344f498) null [15] PADOP (0x34474e0) gvsv GV (0xa76a8) *a UNOP (0x344f428) null [15] PADOP (0x344f460) gvsv GV (0x3327010) *b PVOP (0x344f3b0) trans UNOP (0x3447518) null [15] PADOP (0x3447550) gvsv GV (0x33262d0) *count -e syntax OK
  3. Bits:
    C:\test>perl -MO=Terse -E"$a=int rand 2**64;$b=int rand 2**64; $count += unpack '%32b*', $a & $b" LISTOP (0x33e7460) leave [1] OP (0x33e6e60) enter COP (0x33e74a0) nextstate BINOP (0x33e7508) sassign UNOP (0x33e7548) int [4] UNOP (0x33e7580) rand [3] SVOP (0x33e75b8) const [13] NV (0x32ca498) 1.844674407 +37096e+019 UNOP (0x33e76a0) null [15] PADOP (0x33e76d8) gvsv GV (0x107668) *a COP (0x33e71f0) nextstate BINOP (0x33e7258) sassign UNOP (0x33e7298) int [8] UNOP (0x33e72d0) rand [7] SVOP (0x33e7308) const [14] NV (0x32ca5a0) 1.844674407 +37096e+019 UNOP (0x33e73f0) null [15] PADOP (0x33e7428) gvsv GV (0x32ca510) *b COP (0x33e6ed0) nextstate BINOP (0x33e6f38) sassign LISTOP (0x33e6fa8) unpack OP (0x33e6f78) null [3] SVOP (0x33e7108) const [15] PV (0x32ca600) "%32b*" BINOP (0x33e6fe8) bit_and [12] UNOP (0x33e7098) null [15] PADOP (0x33e70d0) gvsv GV (0x107668) *a UNOP (0x33e7028) null [15] PADOP (0x33e7060) gvsv GV (0x32ca510) *b UNOP (0x33e7140) null [15] PADOP (0x33e7178) gvsv GV (0x32ca5d0) *count -e syntax OK

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In reply to Re^3: Comparing two arrays by BrowserUk
in thread Comparing two arrays by baxy77bax

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