Function fp64_mul_prepare 

pub fn fp64_mul_prepare(
    b: &CircuitBuilder,
    pa: &Fp64Parts,
    pb: &Fp64Parts,
) -> (Wire, Wire, Wire, Wire)

[Block M1] Prepare multiplicands (53-bit) and base exponent/sign.

Build 53-bit multiplicands m_a, m_b and base exponent/sign. Result sign = sign_a XOR sign_b. Base exponent (before normalization adjust): exp_pre = exp_eff_a + exp_eff_b - BIAS.

Parameters

• pa, pb: Parts from fp64_unpack for operands a and b

Returns

• (m_a, m_b, exp_pre, sign) where:
  • m_a, m_b: 53-bit integer significands (with hidden 1 for normals)
  • exp_pre: Base exponent before normalization adjustment
  • sign: Result sign as an MSB boolean