[ntuple] Precision loss for big integer values #416

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1. linev

   self-assigned this

   on Aug 13, 2026
2. linev commented on Aug 13, 2026

   

   linev

   on Aug 13, 2026

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   One can make extra argument for treeProcess function which let keep BigInt values.
   So one get at least all values with TSelector correctly.

   But processing in treeDraw is more complicated.
   There one has several use-cases, and BigInt has to be handled separately.
   Main problem there - use of BigInt in generic arithmetic expressions.
   One cannot simply mix Number and BigInt - unfortunately.
3. undefined-panda commented on Aug 14, 2026

   

   undefined-panda

   on Aug 14, 2026

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   Its unfortunate that there is no elegant way of processing BigInt and Number in JS. Here is a proposal for an extra convertBigInt argument to process rntupleDraw slightly different:

   // in rntuple.mjs
   class ReaderItem {
   
      constructor(column, name, convertBigInt) {
         this.column = null;
         this.name = name;
         this.id = -1;
         this.coltype = 0;
         this.sz = 0;
         this.simple = true;
         this.page = -1; // current page for the reading
         this.convertBigInt = convertBigInt;
      ...
            case kIndex64:
               this.func = function(obj) {
                  const val = this.view.getBigInt64(this.o, LITTLE_ENDIAN)
                  obj[this.name] = this.convertBigInt ? Number(val) : val;
                  this.shift_o(8);
               };
               this.sz = 8;
               break;
            case kUInt64:
               this.func = function(obj) {
                  const val = this.view.getBigUint64(this.o, LITTLE_ENDIAN)
                  obj[this.name] = this.convertBigInt ? Number(val) : val;
                  this.shift_o(8);
               };
               this.sz = 8;
               break;
      ...
   }
   
   async function rntupleProcess(rntuple, selector, args = {}) {
      const {convertBigInt = false, ...restArgs} = args;
      ...
      function addColumnReadout(column, tgtname) {
         const item = new ReaderItem(column, tgtname, convertBigInt);
         item.assignReadFunc();
         handle.columns.push(item);
         return item;
      }
      ...
   }
   
   async function rntupleDraw(rntuple, args) {
      if (isStr(args))
         args = { expr: args };
      else if (!isObject(args))
         args = {};
   
      args.SelectorClass = TDrawSelectorTuple;
      args.processFunction = rntupleProcess;
      args.convertBigInt = true;
   
      treeDrawCall = true;
   
      return readHeaderFooter(rntuple).then(builder => {
         return builder ? treeDraw(rntuple, args) : null;
      });
   }

   Would that be suitable?
4. linev commented on Aug 14, 2026

   

   linev

   on Aug 14, 2026

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   But probably something like args.preserveBigInt. Then default false or undefined will untouch current behavior.
5. linev commented on Aug 14, 2026

   

   linev

   on Aug 14, 2026

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   Fixed in #418
6. linev

   closed this as completedon Aug 14, 2026