git ssb

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const leb128 = require('leb128').unsigned
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const Pipe = require('buffer-pipe')
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const Iterator = require('wasm-json-toolkit').Iterator
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const EXTERNAL_KIND = {
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  'function': 0,
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  'table': 1,
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  'memory': 2,
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  'global': 3
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}
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module.exports = function prepare (wasm, include, symbol) {
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  let globalI64SetterIndex, globalI32SetterIndex, globalGetterIndex, funcSection
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  let numOfFuncs = 0
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  let numOfImports = 0
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  const addedCodeEntries = []
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  const globalsGetterSetters = []
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  const needExporting = {
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    'function': [],
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    'global': []
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  }
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  const it = new Iterator(wasm)
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  for (const section of it) {
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    if (section.type === 'type') {
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      const numOfTypes = section.count
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      // form: func, 1 param, i32, no return
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      const globalI32SetterType = Buffer.from([0x60, 0x01, 0x7f, 0x0])
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      // form: func, 2 param, i32, i32, no return
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      const globalI64SetterType = Buffer.from([0x60, 0x02, 0x7f, 0x7f, 0x0])
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      // form: func, 0 param, i32, 1 return
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      const globalGetterType = Buffer.from([0x60, 0x00, 0x1, 0x7f])
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      section.appendEntries([globalI32SetterType, globalI64SetterType, globalGetterType])
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      globalI32SetterIndex = leb128.encode(numOfTypes)
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      globalI64SetterIndex = leb128.encode(numOfTypes + 1)
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      globalGetterIndex = leb128.encode(numOfTypes + 2)
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    } else if (section.type === 'import') {
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      // parse the import section to build the function indexes
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      const json = section.toJSON()
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      numOfImports = json.entries.filter(entry => entry.kind === 'function').length
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    } else if (section.type === 'function') {
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      // mark functions to be exported
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      numOfFuncs = section.count
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      funcSection = section
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      needExporting['function'] = Array(section.count).fill(true)
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    } else if (section.type === 'table') {
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      needExporting['table'] = true && include.table
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    } else if (section.type === 'memory') {
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      needExporting['memory'] = true && include.memory
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    } else if (section.type === 'global') {
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      const json = section.toJSON()
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      const addedFuncs = []
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      if (!include.globals) {
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        include.globals = new Array(json.entries.length).fill(true)
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      }
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      for (const i in json.entries) {
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        const type = json.entries[i].type
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        const lebIndex = leb128.encode(i)
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        if (type.mutability && include.globals[i]) {
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          if (type.contentType === 'i32') {
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            globalsGetterSetters.push(type.contentType)
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            addedFuncs.push(globalGetterIndex)
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            addedFuncs.push(globalI32SetterIndex)
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            // getter
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            // size, local count, get_global, index, end
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            addedCodeEntries.push(Buffer.concat([
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              Buffer.from([0x03 + lebIndex.length, 0x00, 0x23]),
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              lebIndex,
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              Buffer.from([0x0b])
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            ]))
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            // setter
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            // size, local count, get_local, index , set_global, index, end
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            addedCodeEntries.push(Buffer.concat([
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              Buffer.from([0x05 + lebIndex.length, 0x00, 0x20, 0x0, 0x24]),
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              lebIndex,
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              Buffer.from([0x0b])
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            ]))
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          } else {
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            globalsGetterSetters.push(type.contentType)
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            addedFuncs.push(globalGetterIndex)
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            addedFuncs.push(globalGetterIndex)
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            addedFuncs.push(globalI64SetterIndex)
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            // 64 bit
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            // getter high
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            addedCodeEntries.push(Buffer.concat([
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              Buffer.from([0x07 + lebIndex.length, 0x00, 0x23]),
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              lebIndex,
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              Buffer.from([0x42, 0x20, 0x88, 0xa7, 0x0b])
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            ]))
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            // get low
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            addedCodeEntries.push(Buffer.concat([
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              Buffer.from([0x04 + lebIndex.length, 0x00, 0x23]),
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              lebIndex,
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              Buffer.from([0xa7, 0x0b])
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            ]))
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            // (set_global $b
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            //      (i64.add
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            //        (i64.shl (i64.extend_u/i32 (get_local 0)) (i64.const 32))
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            //        (i64.extend_u/i32 (get_local 1))))
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            // setter
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            addedCodeEntries.push(Buffer.concat([
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              Buffer.from([0x0d + lebIndex.length, 0x00, 0x20, 0x01, 0xad, 0x42, 0x20, 0x86, 0x20, 0x00, 0xad, 0x7c, 0x24]),
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              lebIndex,
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              Buffer.from([0x0b])
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            ]))
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          }
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        }
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      }
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      funcSection.appendEntries(addedFuncs)
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    } else if (section.type === 'export') {
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      // export the memory
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      const addedExports = []
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      if (needExporting['memory']) {
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        const funcExp = generateFuncExport(`${symbol}memory`, 0, 'memory')
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        addedExports.push(funcExp)
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      }
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      // export the table
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      if (needExporting['table']) {
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        const funcExp = generateFuncExport(`${symbol}table`, 0, 'table')
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        addedExports.push(funcExp)
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      }
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      // export functions
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      const funcs = needExporting['function']
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      for (let index in funcs) {
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        index = Number(index)
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        const funcExp = generateFuncExport(`${symbol}func_${index + numOfImports}`, numOfImports + index, 'function')
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        addedExports.push(funcExp)
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      }
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      // export globals
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      let globalFuncIndex = 0
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      for (let index in globalsGetterSetters) {
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        const type = globalsGetterSetters[index]
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        const funcIndex = numOfImports + numOfFuncs + globalFuncIndex
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        if (type === 'i32') {
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          // getter
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          const getter = generateFuncExport(`${symbol}global_getter_${type}_${index}`, funcIndex, 'function')
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          addedExports.push(getter)
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          // setter
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          const setter = generateFuncExport(`${symbol}global_setter_${type}_${index}`, funcIndex + 1, 'function')
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          addedExports.push(setter)
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          globalFuncIndex += 2
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        } else {
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          // i64s
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          // setter high
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          const setterHigh = generateFuncExport(`${symbol}global_getter_${type}_${index}_high`, funcIndex, 'function')
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          addedExports.push(setterHigh)
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          // setter Low
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          const setterLow = generateFuncExport(`${symbol}global_getter_${type}_${index}_low`, funcIndex + 1, 'function')
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          addedExports.push(setterLow)
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          // getter
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          const getter = generateFuncExport(`${symbol}global_setter_${type}_${index}`, funcIndex + 2, 'function')
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          addedExports.push(getter)
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          globalFuncIndex += 3
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        }
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      }
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      section.appendEntries(addedExports)
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    } else if (section.type === 'code') {
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      section.appendEntries(addedCodeEntries)
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    }
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  }
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  return it.wasm
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}
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function generateFuncExport (name, index, type) {
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  const setterHigh = new Pipe()
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  const fieldString = Buffer.from(name)
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  leb128.write(fieldString.length, setterHigh)
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  setterHigh.write(fieldString)
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  setterHigh.write(Buffer.from([EXTERNAL_KIND[type]]))
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  leb128.write(index, setterHigh)
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  return setterHigh.buffer
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}
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