Reduction as comparison

The reduction ∨/ transforms each row into 0 if it contains only zeros and 1 otherwise.

The comparison 0≠ transforms each integer into 0 if its binary representation contains only zeros and 1 otherwise.

      b←1=?1e6 16⍴24            ⍝ 1e6 rows. About half have a 1.
      i←(⊢⊣⎕DR)2⊥⍉b×⍤1⊢¯1*16↑1  ⍝ Two's complement conversion.
      cmpx '∨/b' '0≠i'
  ∨/b → 5.3E¯5 |  0% ⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕
  0≠i → 5.0E¯5 | -6% ⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕

To handle rows whose length doesn't match an integer size (1, 2, or 4 bytes), we read an 8-byte value at an offset and mask off unwanted bytes.