117474c477
move binary encoder to its own package Signed-off-by: Edoardo Vacchi <evacchi@users.noreply.github.com>
49 lines
1.7 KiB
Go
49 lines
1.7 KiB
Go
package binaryencoding
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import (
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"github.com/tetratelabs/wazero/internal/leb128"
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"github.com/tetratelabs/wazero/internal/wasm"
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)
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// encodeCode returns the wasm.Code encoded in WebAssembly 1.0 (20191205) Binary Format.
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//
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// See https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#binary-code
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func encodeCode(c *wasm.Code) []byte {
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if c.GoFunc != nil {
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panic("BUG: GoFunction is not encodable")
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}
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// local blocks compress locals while preserving index order by grouping locals of the same type.
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// https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#code-section%E2%91%A0
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localBlockCount := uint32(0) // how many blocks of locals with the same type (types can repeat!)
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var localBlocks []byte
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localTypeLen := len(c.LocalTypes)
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if localTypeLen > 0 {
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i := localTypeLen - 1
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var runCount uint32 // count of the same type
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var lastValueType wasm.ValueType // initialize to an invalid type 0
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// iterate backwards so it is easier to size prefix
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for ; i >= 0; i-- {
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vt := c.LocalTypes[i]
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if lastValueType != vt {
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if runCount != 0 { // Only on the first iteration, this is zero when vt is compared against invalid
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localBlocks = append(leb128.EncodeUint32(runCount), localBlocks...)
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}
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lastValueType = vt
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localBlocks = append(leb128.EncodeUint32(uint32(vt)), localBlocks...) // reuse the EncodeUint32 cache
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localBlockCount++
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runCount = 1
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} else {
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runCount++
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}
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}
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localBlocks = append(leb128.EncodeUint32(runCount), localBlocks...)
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localBlocks = append(leb128.EncodeUint32(localBlockCount), localBlocks...)
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} else {
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localBlocks = leb128.EncodeUint32(0)
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}
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code := append(localBlocks, c.Body...)
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return append(leb128.EncodeUint32(uint32(len(code))), code...)
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}
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