pj_with_nbits = (PJ_SIZE) => { // Set up a typed array for 2 64-bit floats, and also a view of it as 4 32-bit // integers. Use the first float for the input value, and the second for an // appropriately scaled power of 2 to subtract then add to the value float // to round it to the appropriate bit const flt_arr = new Float64Array([0, 1]); const int_arr = new Int32Array(flt_arr.buffer); const SIGN_MASK = 0x7fffffff; // 0111 1111 1111 1111 1111 1111 1111 1111 const EXP_MASK = 0x7ff00000; // 0111 1111 1111 0000 0000 0000 0000 0000 // HI = 1 on little endian platforms, 0 on big-endian platforms. const HI = little_endian, LO = 1 - little_endian; // use these for rounding values near infinity const LAST_POW2_CUTOFF = 2 ** (PJ_SIZE - 3) * Math.SQRT2; const OVERFLOW_CUTOFF = 2 ** (PJ_SIZE - 1); const INF = 2**31; // use these in the rounding step const HALF_EXP = 1022 << 20; // exponent for 0.5 const ROUND_EXP_OFFSET = HALF_EXP + ((56 - PJ_SIZE) << 20); const float_to_pj = function float_to_pj(flt) { // put the float into our typed array so we can extract its bits flt_arr[0] = flt; // eliminate sign int_arr[HI] &= SIGN_MASK; // special case for numbers near infinity if (flt_arr[0] >= LAST_POW2_CUTOFF) { if (flt_arr[0] >= OVERFLOW_CUTOFF) return INF; const output_abs = ((INF >> (PJ_SIZE - 1)) - INF); return output_abs * ((flt > 0) - (flt < 0)); } // get exponent const flt_exp = int_arr[HI] & EXP_MASK; // round the number to the nearest pj-representable number, ties to even int_arr[2+HI] = ROUND_EXP_OFFSET + (flt_exp > HALF_EXP) * ((flt_exp - HALF_EXP - 0x80000) << 1) flt_arr[0] = (flt_arr[0] - flt_arr[1]) + flt_arr[1]; // get exponent again (might have changed after rounding) const e = ((int_arr[HI] & EXP_MASK) >>> 20) - 1023; // add 1 to small numbers, as we only want to extract the fraction part flt_arr[0] += (e < 0); // fetch 31 bits from the mantissa, put them into "pj" let pj = (((int_arr[HI] << 12) >>> 1) + (int_arr[LO] >>> 21)); // if e > 0, shift to the right and add the appropriate 1s; make space for sign bit pj = ((pj >>> ((e + 1) * (e >= 0))) + (INF >> e) * (e >= 0)) >>> 1; // flip sign for negative input; negative pj numbers have a 2s complement representation pj *= ((flt > 0) - (flt < 0)); return pj; } float_to_pj.inverse = pj_to_float; return float_to_pj; }

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