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The bitwise left shift operator (<<) shifts the binary representation of an integer to the left by a specified number of bit positions. It inserts zero bits into the least significant bit (LSB) positions and discards bits shifted beyond the integer’s fixed width.

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Syntax

int result = operand << shift_amount;
  • operand: The int value to be shifted.
  • shift_amount: An int specifying the number of positions to shift.
  • Return Value: An int containing the shifted value.

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Operational Mechanics

  1. Bit Displacement: Moves every bit in the operand to the left by shift_amount.
  2. Zero Padding: Fills the vacated positions on the right (LSB) with 0.
  3. Arithmetic Equivalent: Mathematically equivalent to multiplying the operand by 2 raised to the power of shift_amount (operand * 2^shift_amount), provided the result does not overflow the platform’s integer limit.

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Platform Specifics and Constraints

Dart handles integer width and shift behavior differently depending on the compilation target (Native vs. Web).

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Dart Native (VM/AOT)

  • Width: Operations are performed on fixed 64-bit two’s complement integers.
  • Shift Count Handling: The shift amount is not masked. Shifting by 64 or more positions shifts all bits out, resulting in 0.
  • Exceptions: Throws an ArgumentError if shift_amount is negative.
  • Overflow: Bits shifted beyond the 64th position are discarded.

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Dart Web

  • Width: Operations map to the JavaScript bitwise left shift. The operand is converted to a signed 32-bit integer before the shift occurs.
  • Shift Count Handling: The effective shift amount is masked to the lower 5 bits (shift_amount & 0x1F). This results in a cyclic shift range of 0 to 31. For example:
    • x << 32 is equivalent to x << 0.
    • x << -1 is equivalent to x << 31 (because -1 in two’s complement has all lower 5 bits set).
  • Exceptions: Does not throw an error for negative shift amounts.
  • Overflow: The result is always truncated to a signed 32-bit integer.

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Example

The following example demonstrates shifting the integer 3 left by 2 positions. 
void main() {
  int value = 3;              // Binary: 0000 0011
  int shift = 2;

  int result = value << shift; // Binary: 0000 1100

  print('Decimal: $result');           // Output: 12
  print('Binary:  ${result.toRadixString(2).padLeft(8, '0')}'); // Output: 00001100
}
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